Chinensis), an Anemophilous Plant

Floral Biology of Jojoba (Simmondsia chinensis), an Anemophilous Plant

Item Type Article

Authors Buchmann, Stephen L.

Publisher University of Arizona (Tucson, AZ)

Journal Desert Plants

Download date 05/10/2021 16:19:18

Link to Item http://hdl.handle.net/10150/554232 Buchmann Jojoba 111

Abstract Floral Biology of Simmondsia chinensis is a widespread perennial plant native to the Sonoran Desert of the United States and northern Mexico. Individuals are dioecious with small Jojoba (Simmondsia unisexual flowers borne on separate plants. The plants are strictly wind- pollinated (anemophilous). Honey bees chinensis), an (Apis mellifera) and native bees often collect large amounts of pollen from male plants but are never found Anemophilous Plant visiting female plants, as there are no floral attractants or rewards in the form of volatiles or nectar, in the green apetalous female flowers. Male plants produce copious amounts of pollen, up to an estimated 523 g /plant, [0.5 -2.4 mg /flower, or 8.3 -48.9 mg /inflorescence]. Per Stephen L. Buchmannl anther there are from 11,000 to 18,000 pollen grains. The USDA Agricultural Research Service pollen is small, smooth with little exine sculpturing and and Department of Ecology and averages 3411 in equatorial diameter. There is almost no Evolutionary Biology surface oily pollenkitt on the grains. Anthers dehisce and University of Arizona pollen is shed during the entire day, but with an early afternoon peak from 1300 to 1500 MST. This corresponds to peak atmospheric concentrations of 60 -63 grains /cubic meter during this period. Seasonal data for Jojoba aerial pollen concentrations and selected hourly values for certain days are also presented for 1982 and 1983 in a native stand. Data on floral number, floral ontogeny, stigmatic receptivity, and seeds per fruit, are also presented for Jojoba. Introduction Since its original description by Johann H. F. Link in 1822 and formal generic placement in 1912 by Camillo Schneider, Jojoba or Goatnut, Simmondsia chinensis (Link) Schneider, has been a source of curiosity and fascination for lay travelers and botanists alike. Jojoba has also been the focus of investigation and no small controversy among plant taxonomists as to the phylogenetic affinity of this plant. Simmondsia is a monotypic genus frequently placed in the Boxwood Family (Buxaceae) or occasionally in the Spurge Family (Euphorbiaceae), or in its own monotypic family, the Simmondsiaceae. The matter is far from settled although recent chemotaxonomic (Scogin, 1981) and anatomical (Gail, 1964; Schmid, 1978) studies suggest keeping Jojoba in the Buxaceae. On the basis of pollen morphology, Nowicke and Skvarla (1984) suggest that Jojoba is unique enough to justify the monotypic family Simmondsiaceae. The natural range of Simmondsia encompasses some 100,000 square kilometers of the Colorado Desert of California, and the Sonoran Desert of Arizona and northern Mexico, primarily Sonora (see Figure 1 in Wallace and Rundel, 1979). Within this area on proper soils and elevations it can be a common element of many xerophytic plant associations. This distribution was first documented in detail by Hastings et al. (1972). The plants are woody perennials from 0.5 -3.0 m tall that may live over 200 years (Gentry, 1958; Yermanos, 1979). For a xerophyte, this species has unusually large sclerophyllous leaves. Information on plant physiology, water relations, photosythesis, and adaptations to stress, 'Address: Carl Hayden Bee Research Center, 2000 E. Allen are now being investigated (Benzioni and Dunstone, Road, Tucson, Arizona 85719 1986). Male Jojoba, as in Figures 1 -5.

Female Jojoba, as in Figures 6 -14. Buchmann Jojoba 113

Jojoba can be found growing on many soils, but usually Twining Malpigh (Janusia gracilis), Triangle -Leaf Bursage alkaline types at elevations from 2,000 to 4,000 feet. It (Ambrosia deltoidea). Also present are Indian -Wheat survives with mean annual precipitation from 3 to 18 ( Plantago insularis), along with numerous grasses and inches. The plant seems to grow in mild climates and is composites, especially Desert Zinnia (Zinnia pumila). Of somewhat frost sensitive (Yermanos, 1979). these plants, the bursage, grasses and Plantago are also In Simmondsia the sexes are separate although her- anemophilous and some individuals of these species were maphroditic plants [ones bearing bisexual perfect flowers] also shedding pollen during our studies. can be found in about 0.01 percent of native plants, es- The second main research area was the mouth of Pima pecially in some coastal populations. This strict dioecy Canyon at the base of the Santa Catalina Mountains, involving imperfect flowers separated in space, imparts a north of Tucson. This site is more mesic than the Carnes forced reliance on a pollen vector for pollination. For Jo- Site and is on a gently south -facing bajada. The plants are joba, like many desert plants, this pollen vector is abiotic. also 2 -3 times larger here than in the Tucson Mountains. Wind is the key to understanding the reproductive biolo- Secondary sites were also observed in the Tucson Moun- gy in this anemophilous (wind -loving) plant. In natural tains. Cultivated eight -year -old plants were also observed populations I have found that sex ratios of male to female during 1982 at the University of Arizona Mesa Agri- plants do not vary significantly from the ratio 1:1. The cultural Center, Mesa, Arizona. plants are, however, widely distributed in an even way Chemical determinations. Pollen for chemical where they occur, this probably being a function of inter - analyses was gathered fresh from mature plants at both specific root competition for soil moisture and nutrients, primary sites by shaking actively- shedding male branches as well as for crown space for light. This interplant spac- into a 60R- opening U.S. standard sieve. Pollen was then ing may in addition to the previous factors represent the air -dried or stored at -20 degrees C prior to analyses. maximum allowable distance still insuring adequate Moisture determinations were made by weighing fresh wind pollination. Until our studies of aerobiology, includ- pollen and then drying it at 60 degrees C until it reached a ing the first measurements of aerial pollen concentrations constant weight. Calorimetry was performed on a Phillip - above native stands (Buchmann, O'Rourke and Shipman, son Oxygen Microbomb Calorimeter (Gentry Instru- 1983), there were no quantitative critical studies examin- ments, Inc., Aiken, SC). Carbon, hydrogen and nitrogen ing the details of wind pollination in Jojoba. values were obtained using a Perkin Elmer Elemental Wind -pollinated plants share several characteristics Analyzer (Model #240) on oven -dried pollen replicates. concomitant with their derived floral morphology and Carbohydrates (sugars and starches) were analyzed color - mode of pollen travel. Copious amounts of pollen are pro- imetrically by a new procedure (Arslan and Matsuda, duced and female flowers often occur on branch tips 1984). Total crude protein was obtained by multiplying where they are exposed to air currents for pollen pick -up the CHN nitrogen values by the customary 6.25 to yield and transport. Many taxa of anemophilous flowers have Kjeldahl protein values. Amino acids were analyzed using evolved elaborate, large surface area, plumose stigmas to 24 -hour hydrochloric acid (in vacuo) hydrolysates with a efficiently capture airborne pollen grains (see Whitehead, Dionex Model #D -300 amino acid analyzer. Stigmatic re- 1969, 1983 for the salient features of anemophily in an- ceptivity was checked by monitoring oxygen bubbles ris- giosperms). Jojoba female flowers have three elongate ing from the stigmatic surfaces when flowers were placed stigmas covered with thin sticky exudate to aid pollen in 3% aqeous hydrogen peroxide (Zeisler, 1938). capture. The flowers are held pendantly on new growth, Aerobiology. Airborne concentrations (grains /cubic but the plants are evergreen, unlike many wind- polli- m) of Simmondsia pollen were quantified at the Carnes, nated species which are deciduous and bloom before the Pima Canyon and Mesa Agricultural Center sites using appearance of a new annual leaf crop. The details of floral two types of pollen sampling devices. These were Ro- morphology and ontogeny in relation to wind pollination torod impaction samplers (Model #82, Ted Brown Assoc., will be given in later sections of this paper. The purpose Los Altos, CA) and a Burkard Seven -Day Recording Vol- of this paper then is to present new data on the reproduc- umetric Spore Trap (Burkard Manufacturing Co., Ltd., tive biology of Jojoba, its aerobiology and characteristics Rickmansworth, Hertfordshire, England). The Rotorod relating to its dependence upon wind for pollination at sampler consisted of two "I bars" or rods coated with selected sites in Arizona. Dow -Corning R 289 silicone grease. These were spun at a fixed rotation rate (2,000 rpm) by a small electric motor. Materials and Methods The Rotorod, like the Burkard, was placed at canopy Field studies were carried out between March, 1981 and height (0.5 -1.0 m) about 1 -2 m from the nearest plants. April, 1984 at two primary sites in Arizona. The main After staining for 24 hours with Safranin "0" in glycerin, field study site was located in the Tucson Mountains 5.3 a cover glass 50 mm in length was placed over the rods in kilometers east of Gates Pass (at 5151 W. Speedway Blvd., a special holder. Raw Rotorod pollen counts were then the Carnes Site) on a gentle north -facing slope. This site transformed to grains per cubic meter (grains /m3) using a is west of the University of Arizona campus, Tucson, formula given previously (see Buchman, O'Rourke, and Pima County, Arizona, and is located in the center of an Shipman, 1983). The Burkard spore trap is an automatic extensive population of Jojoba with only widely scattered clock- driven suction device. It was placed at canopy homes nearby. Other co- dominant plants on the site are height and drew in pollen -laden air at a fixed rate of 10 Ocotillo (Fouquieria splendens), Saguaro (Cereus gi- liters per minute, past a drum which was covered with ganteus), Little -Leaf Rhatany (Krameria parvifolia), adhesive tape. Rotation of the drum was at a constant 114 Desert Plants 8(3) 1987

rate of 2 mm /hr. After exposure, the weekly tapes were flowers lasted about one week during warm dry weather, removed from the drum and cut into daily segments. The with 2 -3 new anthers dehiscing per day (Fig. 16). During tape segments were mounted on microscope slides and cold or wet weather this process is dramatically slowed stained using glycerin jelly containing Basic Fuchsin. Pol- and males may remain upon the plants with apparently len grains were counted and identified at 400X magnifica- no morphological change for 2 -3 weeks. tion. For detailed examinations, magnifications of 625X Morphology and Ontogeny of Female Flowers. and 1500X were sometimes used. Grains were counted Female flowers are much larger than individual male along 0.25 mm wide transects that corresponded to 15- flowers (8 -14 mm long versus 3 -5 mm). They occur singly, minute exposure periods each. Twelve transects 4 mm rarely with two per node or in multiple clusters, on re- apart were counted for each slide to obtain accurate val- curved peduncles so that the entire flowers are borne in a ues of daily pollen concentration. Daily pollen concentra- mostly vertical pendant fashion (Figs. 6, 7, 8, 9). This also tions (as grains /m3) were calculated using the equation for results in the production of pendant fruits. Schmid (1978) Burkard data transformation given elsewhere (Buchman, reports that two (1 -4) large green bracts subtend each O'Rourke, and Shipman, 1983). Aerodynamic analyses female flower. There are also five (4 -6) arcuate foliaceous (i.e. wind tunnel experiments) followed techniques ex- sepals which enlarge to 1 -2 cm shortly after pollination plained by Niklas (1984) and Niklas and Buchmann and are persistent, enclosing the developing fruit (Fig. 15). (1985). The ovary is usually 3- locular (sometimes 4- locular) with axial placentation (with a compitum). The ovules are ana- Results tropous with one per loculus (Figs. 10, 11, 12, 13). The Morphology and Ontogeny of Male Flowers. locules are hollow and air -filled. It requires many weeks Male Simmondsia flowers are small (3 -5 mm in diameter) for the developing seeds to fill these cavities. Usually and united into a capitate inflorescence comprised of only one ovule is fertilized and the other two are aborted from 7 to 36 individual flowers (x = 16 ±6 SD, n = 80). (Fig. 14). The stigma is composed of three, or rarely four, These compact inflorescences are usually produced pen - long (0.5 -1.5 mm), linear, hairy- papillose styles that are dantly (Figs. 1, 2, 3, 4, 5) on new growth toward the out- eventually deciduous (Figs. 8, 9, 10, 11). The fruit is a side of the male plants. The plants are dioecious and the coriaceous, acorn like one -seeded (1 -3) capsule 15 -30 mm male flowers are produced on sessile or very short pedun- long (Figs. 14, 15). Fruit dehiscence is loculicidal. For addi- culate and capitate clusters hereafter referred to as male tional detailed information on floral morphology and his- inflorescences. Male flowers do not have any nectaries or tology, the reader is directed to the paper by Schmid true petals and lack any evidence of an ovary. Both floral (1978). Female floral ontogeny is also mediated by am- bracts and perianth divisions are pubescent with numer- bient temperature. During warm (35 degree C and higher) ous short setae while the stamens (and ovaries in female dry weather the three styles begin emerging from the flowers) are glabrous. Schmid (1978) correctly reports the buds and have reached their full extent 4 -5 days following variable nature between the bracts and the male flowers. anthesis. The stylar branches change from a light -green to The male blossoms (Figs. 4, 5) usually have 5 (range = a yellow -green, presumably during maximum receptivity, 4 -6) distinct angular sepals and a highly variable number then the tips brown and eventually the entire style turns of stamens per flower (Schmid, 1978 reports 8 -16), most brown, loses its moist, sticky appearance and desiccates. literature reporting from 10 to 12. My observations indi- During cold or rainy weather this brown -tip phase may cate a range of 7 -11 with a mean of 10 stamens per flower. last 3 -4 weeks. No scent emanating from either fresh male or female Seasonal Flowering Phenological Patterns. Sim - flowers can be detected by sniffing. This is true even mondsia chinensis may flower as early as January 5 -10 when attempts are made to concentrate any headspace in the Tucson area, and usually flowering begins in late volatiles by placing flowers in a clean glass jar for one January. The peak bloom usually occurs in February and hour at 40 degrees C. Each stamen consists of a short the bloom ends by late February to mid -March. Some (0.25 -0.5 mm) filament and a large erect 4- locular extrorse populations have been observed to bloom at different anther. At anthesis the filaments usually elongate 1 -2 times of the year in response to unseasonal massive pre- mm to place the now exserted anthers above the bracts cipitation. Thus when Tucson recorded 9 inches of rain- and sepals. Anther locule dehiscence is complete along fall during September- October, 1983, some Jojoba popula- the entire stomium, and pollen- shedding is aided by pull- tions responded by near normal frequency of blooms per ing back of locule walls thus fully exposing the pollen. plant during that time. Phenological data (including vege- Pollination is abiotic by wind. tative growth, development of floral buds, flowering and Anthesis for male flowers may occur any time from a fruiting) for three sites in southern Arizona (one near few hours following sunrise to late afternoon. Most Globe, and two near Tucson) were reported by Haase flowers appear to open between 0800 and 1100 MST in (1978). He reported peaks of blooming during April with a Arizona (based upon field observations and hourly aerial lesser peak in May. This author has not seen flowering pollen counts for this time period), although one can find this late in 7 years (1981 -87) of monitoring Tucson additional males opening at almost any hour during populations. daylight hours. During 1983 and 1984 male and female Breeding Systems and Pollination. Simmondsia flowers were individually tagged and their floral ontogeny is dioecious with unisexual male and female flowers monitored from bud to senescence at the Carnes and borne on separate individuals. Plants bearing perfect her- Pima Canyon sites. These data revealed that most male maphroditic flowers are rarely found in certain popula- Buchmann Jojoba 115

Figures 1 -5. Male jojoba (Simmondsia chinensis).1: Terminal branch showing pendant inflorescences with buds prior to anthesis. 2: Male inflorescences at and post anthesis. 3: Closeup of male inflorescence with buds. 4: Closeup of male bud at anthesis but before pollen- shedding. 5: Male flower with anthers actively dehiscing and shedding pollen. tions (A. Kadish, personal communication). Although ap- among ovules for available nutrients, as has been re- omyxis was reported earlier (Gentry, 1955), this is now viewed for other plants (Stephenson, 1981). Sexual dimor- known to be erroneous. Pollination and fertilization must phism and resource allocation (10-15% of their biomass occur to produce fruits with viable seed(s). The minimum for male plants and 30 -40% for females) was examined number of pollen grains needed to impact a female style by Wallace and Runde! (1979). to produce enough pollen tubes to reach the base of the Stigmatic Receptivity. Observations and experi- style and enter the embryo sac is unknown, although un- ments were conducted during 1983 and 1984 to determine der investigation (Buchmann, unpublished). An in -vitro when Jojoba stigmas were maximally receptive. At an- germination medium for Simmondsia pollen tubes was thesis, female flower buds produce three styles which created and tested by Lee et al. (1985). Either the first lengthen approximately 1 -2 mm per day. When these ovule to be fertilized develops into a typical one -seeded styles first emerge from the enveloping bracts (Fig. 7), fruit while the other two abort, or all are fertilized and they are light green in color and bear very little, if any, the plant then aborts the others later for unknown but visible (shiny if present) stigmatic exudate. Stigmatic ex- presumably nutritional reasons. Intense competition may udate is always present, although sometimes difficult to be occurring between developing pollen tubes and also detect, when angiosperms are physiologically receptive.

Figure 15. Floral ontogeny of female flowers from small bud to mature flower to developing and mature fruits.

Table 1. Pollen production (milligrams) per male inflores- This has been demonstrated by Baker and Baker (1973) cence and per flower in two native stands of Simmondsia. and others. At a length of 4 -6 mm, approximately 3 -5 days following anthesis, the styles begin to glisten, ap- Fresh Fresh Weight Weight Number pearing moist and sticky when touched or dusted with a (mg) (mg) inflor. fine powder. This stigmatic exudate is never abundant, Flowers/ pollen/ pollen/ sampled doesn't drip from the styles, and only forms a thin film inflor. inflor. flower (n) over each entire style. The styles appear moist with exu- Carnes site 16 ±Sa 17.0 ±5.9 1.1±0.3 33 date from the time they are about one - quarter of their (Tucson Mtns.) (10 -33)b (8.3 -31.7) (0.5 -1.8) final length until they reach their maximum length. At Pima Canyon 15 ±4 24.5 ±8.3 1.7-0.4 35 (9 -25) (9.5 -48.9) (0.9 -2.4) their greatest length, the styles also have lightened in Grand Means 15.5 ±0.7 20.9 ±8.1 1.4 ±0.5 68 color, now having a yellow -green hue. Stigmatic exudate (9 -33) (8.3 -48.9) (0.5 -2.4) production is highest during the time while the stigmas ¡Values as means plus or minus one standard deviation. remain yellow -green. This period of presumed maximal bRanges given in parentheses. receptivity while the styles are yellowish may last 4 -10 days depending on ambient temperatures at this time. Jauhar (1983) states that generally the stigmas are receptive for only three days; we have found this period can last much longer. At the end of this period the style tips turn brown and gradually desiccate and change color until the entire style lengths are brown and non -receptive. Figures 6 -14. Female Jojoba (Simmondsia chinensis). Preliminary hand pollinations made on bagged flowers 6: Young stem bearing a single pendant receptive female indicate that styles are slightly receptive while the styles flower. 7: Female bud at anthesis with style tips just are green and still lengthening, but that maximum recep- emerging. 8: Mature, fully receptive female flower. tivity occurs when the styles are their longest, are yellow - 9: Closeup of mature female flower showing details of green, and appear moist with exudate. papillate styles. 10: Extreme closeup (ovules are 2 mm Ovule and Seed Counts. Simmondsia typically has long) of sectioned ovary showing conductive tissue and three anatropous ovules per ovary. In wild and cultivated ovules. 11: Sectioned ovary showing shape and size of plants one can also rarely, in perhaps only 1.0% of the locules. 12: Cross section of ovary (looking from apex to ovaries, find four ovules per ovary. Although three ovules base) showing anatropous ovules and locular shape. are normally produced, typically only one of the three 13: Cross section of ovary (looking from base toward ovules will be fertilized, will mature and will eventually apex) showing other end of ovules. 14: Cross section of produce a one -seeded capsular fruit. This is not apparent mature, but still green, fruit showing sepals, pericarp, even 2 -3 weeks after fertilization since the ovules are vascularization, and mature seed (almost entirely made slow to mature and fill the air -filled locular spaces. If up of cotyledons and lacking endosperm) and remnants fruits are cut open at various times post fertilization, one of 2 aborted ovules. ovule of the three gradually enlarges while the other two 118 Desert Plants 8 (3) 1987

Table 2. Estimated number of pollen grains per anther, per flower, per inflorescence and calculated pollen: ovule ratios(x ±SD). pollen:ovule pollen:ovule ratios per ratios (per pollen grains grains per individual inflorescence per anther grains /flowers inflorescence" flower. basis") (n)

Particle counter 14,842 ±3,143 148,420 ±31,430 2,374,720 ±502,880 49,473 -F 10,477 791,573±167,627 4 values for (11,357 -18,120) (113,570 - 181,200) (1,817,120- 2,899,200) (37,857 - 60,400) (605,707- 966,400) acetolyzed pollen Hand counts of 13,712± 1,527 137,120±15,270 2,193,920 ±244,320 45,707 ±5,091 731,307 ±81,440 2 freshly stained (12,632-14,792) (126,320 - 147,920) /2,021,120-2,366,720) (42,107- 49,307) (673,707 - 788,907) pollen Grand means 14,277 ±799 142,770 ±7,990 2,284,320± 127,845 47,590 ±2,663 761,440 ±42,615 6 (11,357 -18,120) (113,570- 181,200) (1,817,120-2,899,200) (37,857- 60,400) (605,707-966,400) aRanges based on a population mean of 10 anthers per flower. bCalculated using a mean of 16 flowers per inflorescence. cSimmondsia has 3, rarely 4, ovules and 3 /flower was used here. d Using values for an average 16- flowered inflorescence. shrink and are eventually resorbed by the fruit. By the per inflorescence, the results are even more impressive, time fruits have reached their maximum size, the two with a range of 1,817,120 to 2,899,200 pollen grains for an aborted ovules are mere remnants between the greatly inflorescence with 16 flowers (Table 2). Cruden (1976, enlarged cotyledons and fruit wall (Fig. 14). At this time it 1977) has calculated pollen:ovule (PO) ratios for many is not clear whether all three ovules are fertilized with angiosperms with a diversity of primary pollinators and two being aborted later, or whether it is the first ovule to reproductive biologies. He finds that insect -pollinated be fertilized that matures. Females seem to retain or abort plants have intermediate PO ratios (1,000 -20,000), precise already fertilized fruits depending on water and intraplant systems like milkweeds and orchids have very low PO's nutrient status (Stephenson, 1981). Fruits set early in the (hundreds), while the pollen:ovule ratios for wind- polli- season are more likely to be retained than those set later nated plants are extremely high (20,000 -100,000 or even when plants already bear large fruit loads. more). I calculated a value of 37,857 -60,400 grains per A total of 4,740 fruits randomly selected from 55 plants ovule (x= 47,590 ±2,663 SD) for Jojoba (Table 2). Sim - representing both the Pima Canyon and Carnes sites were mondsia then has a typical PO ratio falling within cut open and scored for being one -, two -, or three -seeded. Cruden's values for other anemophiles. Many anthecolo- The results confirmed my general impression that one- gists in addition to Cruden now rely on pollen:ovule seeded fruits are typical for this species. Of the 4,740 fruit ratios as sensitive indicators of the type of breeding sys- sample, 88.2% were single- seeded, 11.2% were double, tem a plant has and how precise and efficient pollination and only 0.5% were three -seeded. This pattern has been is likely to be. observed by other Jojoba workers (Lee and Palzkill, per- Pollen Germinability. Pollen viability is usually sonal communication). That many more two -and three - judged by staining pollen grains, typically with Cotton seeded fruits are not produced may be related to inade- Blue in lactophenol, which stains callose. Measurements quate levels of pollination or fertilization, or to intra- using this stain reveal pollen viability (stainability) to be ovarian competition for available nutrients within the de- 70 -95 %. Recently an in -vitro agar pollen germination veloping fruits (Stephenson, 1981). No increase in total medium has been developed (Lee, 1982) and is still being seed biomass is apparent in two- or three -seeded fruits improved upon (C. W. Lee, personal communication). relative to single- seeded ones, the seeds being simply one - This technique is an advance over simple Cotton Blue half or one -third the mass of those with only one seed per staining which only indicates whether callose is present, fruit. We still have no data on what proportion of the not whether the grains are actually viable and will germi- female flowers per plant eventually mature fruits, nor the nate. Fresh pollen placed on the artificial agar medium fraction of immature fruits that are lost to abortion or commonly gives values of 80 -95% germinability (Lee, insect parasitism. Jauhar (1983) states that 5 -30% of the 1982; Lee and Buchmann, unpublished). Recently we (Lee female flowers abscise either before or after fertilization. and Buchmann, unpublished) have found that certain Pollen Production and Pollen:Ovule Ratios. wild and cultivated male plants produce pollen far less Like many anemophilous plants, Simmondsia produces germinable (30 -60 %) than typical for the species. vast quantities of pollen, per flower and per plant (Tables Whether these low germinability percentages are due to 1, 2). Wind pollination is not directional or precise, so is genetic or environmental causes is unknown. wasteful of pollen. The vast majority of pollen grains pro- Pollen Chemistry. We (Buchmann and Schmidt, un- duced will not reach their stigmatic targets, having been published) have conducted chemical analyses on hand - intercepted by intervening stems, leaves or ground or cap- collected Simmondsia pollen. These results will be sum- tured by rain (Whitehead, 1969, 1983). Thus it is necessary marized here and fully developed elsewhere. Simmondsia for these plants to produce many more pollen grains than pollen contains 31 -34% total crude Kjeldahl protein ovules. Simmondsia anthers contain 11,000 -18,000 grains (4.91 -5.53% nitrogen), which is high compared to most per anther (x = 14,277 ±799) and 113,000 to 181,000 grains typical anemophiles. The pollen energetic value is also per flower (x= 142,770 ±7,990 SD) (Table 2). Expressed high, with 5,838 ±27 (SD) calories /gram. The pollen is Buchmann Jojoba 119

All anthers 0-C1 One or more anthers 20 - Pp.

ca I5

o ó I0 .o E z

3 4 5 6 Days with anthers dehiscing

Figure 16. Details of male floral ontogeny. The relationship between number of tagged observational flowers (Pima Canyon, 1982) that either had all or one or more anthers dehiscing on days 1 -8 following floral anthesis. relatively non -sticky with little oily pollenkitt, although matic effect of raindrop capture of pollen (McDonald, internal lipids are present. The pollen is starchless (termi- 1962). Note that in Figure 17 pollen concentrations nology of Baker and Baker, 1979), containing only lipids as reached a daily maximum (1,128 grains /m3) on March 20, energy storage reserve products. Total soluble carbohy- 1981. Subsequent daily maxima were 835 grains /m3 on drates comprise 15.2% of the total pollen dry weight with March 21, 535 grains /m3 on March 22, and 641 grains /m3 high levels of sucrose, glucose and fructose present. Pol- on March 23. The highest daily (1,128 grains /m3) and len was also hydrolyzed and at least 17 amino acids were hourly (267 grains /m3) values occurred on March 20, 1981 present in large amounts. Amino acid and protein data just before two rainstorms. Following the rainy period the will be presented elsewhere in a paper describing Sim - pollen counts dropped dramatically until present in negli- mondsia pollen chemistry. gible amounts (only 7 grains /m3 /hour). Airborne pollen Jojoba blooms very early in the season when there are abundance was dramatically lowered for at least 18 hours few other pollen sources available to perennial honey bee after these two storms. Other authors have noted this colonies, or to early spring native bees. Although not vis- "pollen washout" phenomenon (Gregory, 1961; iting the female flowers, honey bees collect large McDonald, 1962; Tauber, 1965; Whitehead, 1983). amounts of Simmondsia pollen. Details of this relation- Burkard data from the Carnes Site for the 1983 season ship were examined by Schmidt and Buchmann (1983). (Fig. 18) reveal pollen abundance values similar to those Aerobiology of Pollen. A paper describing pollen of 1981. Daily maxima ranged from lows of 250 to 1,003 concentrations at canopy level (1 meter) above the Carnes grains /m3 at the beginning and end of the bloom, with Site in 1981 were made using Burkard and Rotorod maxima ( >250 grains /m3) during the peak bloom. Pre- samplers (Buchmann et al., 1983). These authors found cipitation washout again played an important role in that daily Jojoba pollen concentrations varied from 69 lowering aerial pollen concentrations. Pollen was cap- grains /m3 to 1,128 grains /m3. Pollen from 14 other ane- tured by the Burkard trap even when we could not find mophiles was also quantified. For a five -day sampling any males within the population that were actively shed- period during peak bloom, Simmondsia represented ding pollen. Either there were undetected low numbers of 55.7% of the total pollen grains captured (or 3,728 grains males we did not find, or Simmondsia pollen was being of the total 6,699 grains). The hourly Simmondsia values carried in from more distant populations phenologically varied from 7 grains /m3 to 267 grains /m3. In every case earlier than the Carnes Site. The peak pollen abundance the abundance of airborne Jojoba pollen was greater dur- occurred from February 26 to March 6, 1981. By March 14, ing daylight hours. Minimum values always occur at 1981 there was virtually no airborne Simmondsia pollen night since air masses are usually less turbulent at this present. time and particles settle rapidly out of the troposphere Laboratory studies during the 1984 field season (Niklas under these conditions (Gregory, 1961). Figure 17 has been and Buchmann, 1985) were conducted to determine aero- redrawn from Buchmann et al. (1983) to illustrate the dra- dynamic properties of female Jojoba flowers when 300

250

200 E / Night Precipitation

ó,150 ac ó Q_ 100

50 l

0 00 0 00 00 0 00 00 0 000000 000 0 O O 00 0000 0 0 0 0 O 0 0 O N CO 0 N 00 N N N Ñ OO Ñ Ñ 00 Ñ 00 Ñ 00 3/19 3/20 3/21 3/22 3/23 3/24 Date and time Figure 17. Pollen aerobiology curve for Simmondsia chinensis (redrawn from Buchmami, et al., 1983) from Pima Canyon (1981). Pollen concentrations fall off dramatically at night. The washout effect of precipitation (on March 20, 1981) can be seen.

"flown" in a wind tunnel and impacted with fresh Jojoba ated by foliage leaves, and by smaller -scale airflow pat- pollen or helium filled neutral density bubbles. Airflow terns, formed around and by the floral bracts and stigmas. patterns around styles, stems, and bracts along with im- These patterns are visualized in Figure 20 where the lines paction areas and capture efficiencies were qualitatively and arrows represent averaged flow patterns from wind and quantitatively examined using orthogonal strobo- tunnel stroboscopic images of pollen grains passing by, scopic cinematography (see methods in Niklas, 1983, 1984). impacting, and otherwise interacting with female Aerodynamics of Wind Pollination in Sim - flowers. Interestingly, the upright leaf pair at each node mondsia. We (Niklas and Buchmann, 1985) recently be- and above carpellate flowers deflected the trajectories of gan field and laboratory wind tunnel analyses designed to nearby grains, intersecting ambient airflow at 90 degree examine the functional /morphological relationship of Jo- angles, causing intense downward "pollen showers" onto joba branches and female flowers in relation to adapta- the decumbent female flowers. This was an unexpected tions to anemophily in the species. Simmondsia is result of our wind tunnel aerodynamic studies. Subtend- thought to have had an entomophilous ancestry (Gail, ing floral bracts and sepals also affected airflow patterns 1964; Gentry, 1958). Branches from living female plants around female flowers. Branch systems with their leaves were placed into the exhaust cone of a wind tunnel and experimentally removed, however, decreased pollination bombarded with viable conspecific pollen or pollen -sized efficiency (pollen capture by stigmas), by more than 50% neutral density helium -filled soap bubbles to determine (Niklas and Buchmann, 1985). pollen- capture efficiency and to visualize turbulent air- Traditionally, wind -pollinated plants are thought to flow patterns around leaves and flowers (see Niklas, 1984 have evolved to reduce the amount of "inert" (non - and Niklas and Buchmann, 1985 for technical details). reproductive) surface area such as leaves, and to bloom The behavior of airborne pollen grains (their trajectories before leaves are expanded in the Spring. Simmondsia and velocities) was quantified around individual never sheds all of its leaves simultaneously, therefore branches, leaves and near carpellate flowers. Pollen flowering when fully leafed. In contrast, Niklas and deposition (capture) onto the three long stigmas was in- Buchmann (1985) quantitatively demonstrated that the fluenced both by large -scale aerodynamic patterns, gener- foliage (leaves) of Jojoba actually increases the amount of 120

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I I I I I I/ / I I I I I 'till II 15 22 29 7 14 21 28 7 14 21 28 Jan. Feb. March Date Figure 18. Complete Burkard seasonal aerial pollen concentration (grains /m3) for the Carnes (Tucson Mountains) site during 1983.

pollen brought into floral airspaces and actually orients ments (e.g. adequate inter -row spacing for tillage, irriga- pollen grain trajectories toward receptive stigmas. If pol- tion, and herbicide applications). There is also no indus- len grains are not captured the first time they may remain try-wide standardization for how many males must be tumbling in vortexes for many seconds before being fi- planted to pollinate X number of females. Some growers nally captured by that flower, shed to another in the lin- have even planted large acreage blocks of all female ear progression toward the shoot apex, or lost to large - plants. Many growers have decided that a 20:80 ratio of scale air patterns. Clearly, not all anemophilous plants male:female is optimal. This ratio will likely work but is simply shed their pollen in massive amounts and hope for based on no sound pollination data and may indeed be the best. Some, like Simmondsia, have evolved adapta- suboptimal with respect to pollination values with other tions (e.g. reduction in flower number, peduncle elonga- planting arrangements. Considerations for an optimal or- tion, and sepal curvature) selectively advantageous since chard geometry, for maximum pollination, are in a state these features aerodynamically enhance the probability of of preparation ( Buchmann, unpublished). pollen capture by stigmas over nearby inert leaf surfaces. Other morphological features of Simmondsia, such as Discussion leaf morphology and number and retention of leaves dur- Qualitative and quantitative aspects of pollen aerobiol- ing flowering, have remained unaltered (since develop- ogy and features of anemophily in Simmondsia chinensis mental and other selective forces are simultaneously op- were studied in both natural and cultivated populations erative), and might be termed "exaptations" in the sense for the first time. This and an earlier study (Buchmann, of Gould and Vrba (1982). We may find with further O'Rourke and Shipman, 1983) documented the total de- study, other plants, like Simmondsia, which have pendence of warm, dry weather and dependable winds for evolved selectively advantageous specific responses to the the pickup, distribution and deposition of pollen on challenges of that controllable chaos we call wind pol- female flowers, leading to fertilization and fruit set. The lination. For a further discussion see Niklas (1985a, earlier hypothesized role of apomixis in the reproductive 1985b). biology of Jojoba (Gentry, 1955) is without support. Al- Agronomic Considerations. Until now Jojoba though Simmondsia is dioecious, female flowers require growers have only been concerned with row spacing and adequate levels of pollen on stylar arms ( "stigmatic load- male:female ratios based only upon cultural crop require- ing"), from neighboring males to set fruits. No evidence 122 Desert Plants 8(3) 1987

for biophysical calculations relating to settling velocities 60 and pollen capture by female stylar arms at different wind velocities (Niklas and Buchmann, 1985). Chemical analyses of pollen for total crude protein, car- 50 bohydrates and calories per gram revealed pollen unusually rich in these components compared with pollen from other anemophiles (Colin and Jones, 1980; E 40 Buchmann, unpublished). Pollen from most wind- polli- u, nated plants contains far less (3 -20% crude Kjeldahl pro- 0 tein) than the Simmondsia with its 34% protein 30 (Buchmann, unpublished). Other chemical data show similarly high levels in comparison with other wind -pol- a) linated plants. Could the reason for these high levels be 20 the phylogenetic constraint of Simmondsia's ancestral reproductive biology? Hermaphroditic perfect flowers are relatively rare in inland extant populations, but are more 10 common in some coastal populations that may represent the original area of origin for the genus (A. Kadish, personal communication). If Simmondsia originally had per- o I 1 I I I I I l I I I

I 3 5 7 9 I I 13 15 17 19 21 23 fect flowers and only secondarily became dioecious, then Hours it is entirely reasonable to assume that it had in the past, Figure 19. Mean hourly pollen concentrations (grains/ showier flowers that were insect pollinated. Thus, al- m3) from 5.3 km east of Gates Pass, Tucson, Arizona though pollen morphological features may reflect second- using the Burkard sampler. Values are mean hourly ary adaptations to anemophily (i.e. small size, non -sticky counts for a 69 -day period, from January 15 to March 25, with little pollenkitt, and almost no exinal sculpturing), 1983. its chemically rich pollen may be a character left from a time when the species was insect -pollinated. Alter- was found for either apomixis or parthenocarpic fruit natively, Simmondsia may have always been ane- development. mophilous, and simply represents higher chemical levels Pollen from anemophilous species is generally smaller and presumably a nutritious pollen for the few bees (Apis than from entomophilous taxa, with equatorial diameters mellifera, some halictids and anthophorids), and flies ranging from 20 to 40µ (Whitehead, 1983). Simmondsia (Syrphidae) that have learned to exploit its pollen as a pollen has mean equatorial diameters from 30 to 60µ (No- food item. wicke and Skvarla, 1984; Martin and Drew, 1969; Pollen production on a single anther, flower, and in- Buchmann, unpublished). Its pollen is also non -sticky, florescence basis was presented confirming the large having a minute layer of oily pollenkitt. The pollen is amount of pollen produced by male plants. Pollen must released as monads although depositional patterns on be produced in great quantities ensuring that enough Burkard tapes and Rotorods suggest some degree of reaches the small targets that are female flowers. Almost clumping (2 -8 grains) during flight for a small proportion, all of the pollen that becomes airborne will impact upon possibly 2 -5% of the pollen grains. Their shape is spheri- stems, leaves, ground, be carried away by the wind, or be cal to sublobate to subprolate, with the amb triangular, washed out of the atmosphere by precipitation. Unlike tricolporate with large, slightly ovate poorly defined ger- most other anemophilous plants, which produce male minal apertures. The tectum is irregularly scabrate some- and female flowers before leaf blades are fully expanded, times with small "islands" with spinules (Nowicke and Jojoba is evergreen with a full component of thick leaves Skvarla, 1984). Earlier (Martin and Drew, 1969) and very present at all times. These leaves should act to impact recent studies (Nowicke and Skvarla, 1984) used air -dried and filter out substantial quantities of airborne pollen pollen powdered onto a scanning electron micrography which would otherwise have been available for pollina- (SEM) stub, or acetolyzed grains which were then sputter - tion (but see Niklas and Buchmann, 1985). To partially coated for scanning electron microscopy. I suggest that counteract pollen loss and other factors, plants may have prolate or subprolate shapes given for Simmondsia are responded by producing far more female buds and flowers artifacts of specimen preparation for SEM due to desicca- than will ever be pollinated, fertilized, or that have tion and beam damage, as has been suggested as a cau- enough nutrients and /or water to bring those fruits to tionary note for pollen SEM preparation in general by maturity. Large numbers of floral buds are produced in Lynch and Webster (1975). When pollen grains are caught wild and cultivated plants that never will be pollinated, on microscope slides bearing double -stick tape or silicone or will abort for some physiological reasons later. In Jo- grease, then viewed immediately, their shape is decidedly joba this may range from 30 to 90 percent of the original spherical. At the time of pollen shedding and wind -medi- flowers present (D. A. Palzkill and C. W. Lee, personal ated takeoff, the pollen is fully hydrated containing at communication). least 82 -90% moisture. That the pollen is truly spheroi- Why so many single- seeded fruits are produced is also dal and not prolate during airborne transport is important an open question. The energetic, dispersal and seedling Buchmann Jojoba 123

Figure 20. Schematic summaries of observed pollen grain trajectories generated around branches, leaves and flowers in wind tunnel experiments. Pairs of upright leaves above each female flower deflect pollen grains into trajectories that can shower flowers and stigmas with pollen, aiding capture (left). When leaf pairs were experimentally removed, however, this caused somewhat different leeward turbulence patterns (right). With- out their leaves, stigmas captured only one half as much pollen as unmodified control flowers. establishment adaptive values of one, two, or three -seed- flowers to confirm these chemical tests. edness in Simmondsia is not known. Proximate and ulti- It is hoped that commercial Jojoba growers realize how mate causes of pollination /ovule fertilization and fruit dependent economical fruit development is upon ade- abortion are also unknown at this time. Simmondsia quate pollination levels, and how little we actually know should prove to be an excellent plant in which to study about the processes from floral bud development to pol- the interaction of male and female function as it relates lination and fertilization, ultimately leading to abundant to "female choice" for mates and intraplant decisions to mature fruits per plant. Fruit abortion levels either due to abort some or all of its yearly fruit crop. Even given ade- insufficient pollination or intraplant physiological, genet- quate equal levels of pollination every year, such long - ic or external environmental factors (soil moisture, favor- lived perennials may have long multiple annual bio- able ambient temperatures) can be extremely high and we rhythms (circannual) of fruit production of which we are have yet to discover their cause(s). Only through basic as yet totally unaware. research on the reproductive biology of this plant can Stigmatic receptivity is correlated with the presence of important agronomic questions be answered, that will en- stigmatic exudate and stigmas are maximally receptive at sure the worldwide development of Jojoba as a major crop their greatest length and when the styles are a yellow - for arid lands. green without any brown on the tips. Based on hydrogen peroxide (peroxidase tests) the entire surface areas of all Acknowledgments three styles from tips to bases are apparently receptive. I thank Chi Won Lee, David A. Palzkill, LeMoyne Peak stigmatic receptivity is very dependent on ambient Hogan, Mary K. O'Rourke, Karl J. Niklas and Justin O. temperatures prior to anthesis and during bloom. During Schmidt for their constructive criticisms of this or an warm weather female floral buds mature quickly and earlier draft of this manuscript. Special thanks to David may remain receptive for as long as 3 -6 days. Cold tem- Ring (Biomedical Communications) for the photographs peratures retard or halt floral development or ontogeny and to Marlo D. Buchmann for the figures. Field assis- and females appear to be receptive for up to several tance throughout the project was given by Charles W. weeks, based upon their length, proper color, and moist Shipman (Carl Hayden Bee Research Center), without appearance. Hand pollinations must be made on bagged whom this study would not have been possible. 124 Desert Plants 8(3) 1987

Literature Cited Baker, H. G., I. Baker, and P. Opler. 1973. Stigmatic exudates and Lynch, S. P. and G. L. Webster. 1975. A new technique of prepar- pollination. pp. 47 -80 in N. B. Brantjes (ed.), Pollination and ing pollen for scanning electron microscopy. Grana 15: Dispersal. Dept. of Botany, University of Nijmegen. 127 -136. Netherlands. Martin, P. S. and C. M. Drew. 1969. Scanning electron micro- Baker, H. G. and I. Baker. 1979. Starch in angiosperm pollen graphs of southwestern pollen grains. J. Ariz. Acad. Sci. 5(3): grains and its evolutionary significance. Amer. J. Bot. 66: 147 -176. 591 -600. McDonald, J. E. 1962. Collection and washout of airborne pollens Benzioni, A. and R. L. Dunstone. 1986. Jojoba: Adaptation to and spores by raindrops. Science 135: 435 -437 environmental stress and the implications of domestication. Niklas, K. J. 1983. The influence of paleozoic ovule and capsule Quart. Rev. Biol. 61(2): 177 -199. morphologies on wind pollination. Evolution 37(5): 968 -986. Buchmann, S. L., M. K. O'Rourke, and C. W. Shipman. 1983. Niklas, K. J. 1984. The motion of wind borne pollen grains Aerobiology of pollen abundance and dispersal in a native around conifer ovulate cones: Implications on wind pollina- stand of jojoba (Simmondsia chinensis) in Arizona. pp. 79 -92, tion. Amer. J. Bot. 71: 356 -374. in jojoba and its Uses Through 1982. Proceedings of the Fifth Niklas, K. J. 1985a. The aerodynamics of wind pollination. Bot. International Conference. Oct. 11 -15, 1982. Tucson, Arizona. Rev. 51(3): 328 -386. Colin, L. J. and C. E. Jones. 1980. Pollen energetics and pollina- Niklas, K. J. 1985b. Wind pollination -A study in controlled tion modes. Amer. J. Bot. 67(2): 210 -215. chaos. Amer. Scientist 73: 462 -470. Cruden, R. W. 1976. Fecundity as a function of nectar production Niklas, K. J. and S. L. Buchmann. 1985. Aerodynamics of wind and pollen -ovule ratios. pp. 171 -178 in J. Burley and B. T. pollination in Simmondsia chinensis (Link) Schneider. Amer. Styles (eds.), Tropical Trees: Variation, Breeding and Conser- J. Bot. 72(4): 530 -539. vation. Academic Press. New York. Nowicke, J. W. and J. J. Skvarla. 1984. Pollen morphology and the Cruden, R. W. 1977. Pollen -ovule ratios: a conservative indicator relationships of Simmondsia chinensis to the order Euphor- of breeding systems in flowering plants. Evolution 31: 32 -46. biales. Amer. J. Bot. 71(2): 210 -215. Gail, P. A. 1964. Simmondsia chinenesis (Link) Schneider: Anat- Regal, P. J. 1982. Pollination by wind and animals: Ecology of omy and Morphology of flowers. Unpublished M. A. Thesis, geographic patterns. Ann Rev. Ecol. Syst. 13: 497 -524. Claremont Graduate School, Claremont, California. Abstract Schmid, R. 1978. Floral and fruit anatomy of jojoba (Simmondsia in Bull. New Jersey Acad. Sci. 11: 43 -44. chinensis). pp. 143 -148 in La Jojoba: Memorias de la II Con - Gentry, H. S. 1955. Apomyxis in black pepper and jojoba. J. of ferencia Internacional Sobre la Jojoba y sue Approvechamien- Heredity 46(1): 8. to. Ensenada, Baja California Norte, Mexico, 10 al 12 Febrero Gentry, H. S. 1958. The natural history of jojoba (Simmondsia de 1976. Consejo Nacional de Ciencia y Technologia, Comi- chinensis) and its cultural aspects. Econ. Bot. 12(3): 261 -295. sion Nacional de las Zonas Acidas. Consejo Internacional So- Gould, S. J. and E. S. Vrba. 1982. Exaptation -a missing term in bre Jojoba. Mexico. 340 pp. the science of form. Paleobiology 8: 4 -15. Schmidt, J. O. and S. L. Buchmann. 1983. Jojoba -An excellent Gregory, P. H. 1961. The Microbiology of the Atmosphere. little -known pollen plant for bees. Amer. Bee J.123(5): Leonard Hill Books Limited. London; Interscience Publishers, 379 -382. Inc. New York. 251 pp. Scogin, R. 1980. Serotaxonomy of Simmondsia chinensis (Sim - Haase, E. F. 1978. Phenology of some native jojoba populations in mondsiaceae). Aliso 9(4): 555 -559. Arizona. pp. 39 -47 in La Jojoba: Memorias de la 11 Conferen- Stephenson, A. G. 1981. Flower and fruit abortion: Proximate cia Internacional Sobre la Jojoba y sue Approvechamiento, causes and ultimate functions. Ann. Rev. Ecol. Syst. 12: Ensenada, Baja California Norte, Mexico, 10 al 12 Febrero de 253 -279. 1976. Consejo Nacional de Ciencia y Technologia, Comision Tauber, H. 1965. Differential pollen dispersion and the inter- Nacional de las Zonas Acidas, Consejo Internacional Sobre Jo- pretation of pollen diagrams. Dan. Geol. Unders., JAfh.J Racke joba. Mexico. 340 pp. 2, No. 89, pp. 1- 70. Hastings, J. R., R. M. Turner, and D. K. Warren, 1972. An Atlas of Wallace, C. S. and P. W. Rundel. 1979. Sexual dimorphism and some Plant Distributions in the Sonoran Desert. Tech. Rept. resource allocation in male and female shrubs of Simmondsia Meteor. Climat. Arid Regions No. 21. Inst. Atmos. Physics. chinensis. Oecologia 44: 34 -39. University of Arizona. Tucson. Whitehead, D. R. 1969. Wind pollination in the angiosperms: Jauher, P. P. 1983. Cytogenetic studies in relation to breeding Evolutionary and environmental considerations. Evolution 23: superior cultivars of jojoba. pp. 63 -77 in Jojoba and its Uses 28 -35. Through 1982, Proceedings of the Fifth International Jojoba Whitehead, D. R. 1983. Wind pollination: Some ecological and Conference. Oct. 11 -15, 1982. Tucson, Arizona. evolutionary perspectives. pp. 97 -108 in L. Real (ed.), Pollina- Lee, C. W. et al. 1982. In vitro germination and cryogenic storage tion Biology. Academic Press, Inc. New York. 338 pp. of jojoba pollen. pp. 347 -351 in M. Puebla (ed.), Memories: IV Yermanos, D. M. 1979. Jojoba. A crop whose time has come. Reunion Internacional de la Jojoba. Consejo Internacional de Calif. Agric. 33(7 -8) 4 -7, 10 -11. la Jojoba. 493 pp. Zeisler, M. 1938. Uber die Abgrenzung der eigentlichen Narben Lee, C. W., J. C. Thomas, and S. L. Buchmann. 1985. Factors flache mit Ailfe von Reaktionen. Beih. Bot. Zentralbl. A. 58: affecting in vitro germination and storage of jojoba pollen. J. 308-318. Amer. Soc. Hort. Sci. 110(5): 671 -676