sign in sign up
<<
Home , Argyroderma, Fenestraria, Frithia, Lithops

Downloaded from http://online.ucpress.edu/abt/article-pdf/30/3/201/23957/4442008.pdf by guest on 02 October 2021

The Xerophytic Mimicry

* John A. Jump, ElmhurstCollege, Elmhurst,Illinois

Certain easily grown of the family provide demonstrationsof mimicry, adaptationto intense light and drought, and dispersal by ,

For the past fifteen years the author has The plants are easily grown in a sunny win- kept in cultivation a collection of plants of dow or under Gro-Lux tubes; they are the family Aizoaceael which is easily grown flowered readily in a greenhouse; and the and admirably suited to demonstration of are as easily germinated as petunias some of the most remarkable of although they have a long juvenile period. the kingdom. At present the group The family is predominately found in the is not widely available commercially, al- deserts of south-west , the Karoo though an occasional specimen shows up and Kalahari being particularly rich in vari- in succulent collections at garden centers ety of species. Largely for this reason, most and on the plant counters of some of the of the available literature on the group is chain stores. Seeds in mixture and plants by English, German, and South African au- are available from at least one source in thors, the foremost semi-popular works being this country and may be obtained readily Higgins' translation of Schwantes,' "- from abroad in a wide of species. ing Stones and Mid-Day ," and the tri-lingual, "Mesembryanthema," by Brown, 'European writers tend to use Mesembryanthema- ceae rather than Aizoaceae. Tischer, Karsten, and LaBarre.

201 Mimicry brown, with shades of gray and violet being Mimicry, which is such a common phe- common. The definitive monograph of the nomenon in the animal kingdom, is quite by Nel lists fifty species, but addition- rare among plants and perhaps is most al ones have been subsequently discovered. classically illustrated by a few orchids that In nature most of the species grow buried are pollinated as a result of the attempted in the substrate with just the tops of the copulation by certain bees and wasps which exposed, but in our local conditions they mimic. Mimicry plants of the Aizoaceae of less intense light, the majoritygrow with resemble a wide variety of rock fragments the pair partially or entirely above the and pebbles in their markings, contours, and level. Each year a new leaf pair is coloration. They are highly succulent and formed at right angles within the old pair, presumably would be destroyed quickly as and the old pair gradually withers as it is a water source by indigenous animals if replaced. Schwantesreports that some plants

they were more readily visible. The group have been determined by leaf base count Downloaded from http://online.ucpress.edu/abt/article-pdf/30/3/201/23957/4442008.pdf by guest on 02 October 2021 which is the prime example of mimicry is to be at least 95 years old. The flowers are the genus , (Fig. 3), called "stone composed of numerous staminodes and are face" in some American catalogues, and either white or yellow in color, (Fig. 4). "Hottentot's backside" by the imaginative The similarity of the flowers has made it Boers. These plants are virtually stemless necessary to base the different species pri- and consist of a single pair of leaves sep- marily on the basis of the shape and color arated by a more or less distinct cleft. They patternof the plant body. vary in color from green to rusty-red and Less varied than the foregoing genus, but

J4~~~~~

...~ .....j~~~~~~~~~~~~~~~~~~ ..... ~~ ~~~ .

Fig. 1. Plant of sp. Fig. 2. Plant of Pleiospilos sp. with two granite pebbles in upper and lower left.

Fig. 3. Four species of Lithops. Fig. 4. Flowers, leaves and of Lithops kuibisensis.

202 The American Biology Teacher, March, 1968 highly convincing as mimicry plants are the haps the most intricate seed dispersal mech- granite-like species of Pleiospilos, (Fig. 2), anisms to be found in the plant kingdom, or "split rocks" as they are commonly called. and their structure has been treated in detail Some of these have several pairs of leaves by several authors. When the woody capsule on the plant at a time, but the observer is fully ripe, a process that may require a must look closely to decide which are leaves number of months, the upper surface splits and which are pieces of stone, if they have into five or more sectors which are the valve been grown among fragments of granite. lids. These remain tightly closed, (Fig. 5), Several species of these occasionally show until moistened by several drops of water. up on the counters of shops dealing in The water penetrates the capsule and is succulent plants, and they produce their absorbed by the highly hygroscopic mucilage large brilliant yellow flowers quite readily which is contained in cells of a palisade-like in a greenhouse or in a sunny window. A tissue beneath the valve lid. The swelling

third genus to add variety might be the of these hygroscopic keels forces the valve Downloaded from http://online.ucpress.edu/abt/article-pdf/30/3/201/23957/4442008.pdf by guest on 02 October 2021 silver skins, Argyroderma (Fig. 1), which lids upward and backward until the seed produce a single pair of leaves like Lithops cavities are exposed (Figs. 6, 7, 8). Sub, but are perfectly smooth, rounded and sequent drops of water falling as rain with unmarked, mimicking grayish white, quartz considerable impact will cause the locules pebbles almost perfectly. Of the latter two to function as splash cups, and the seeds genera, Pheispilos bolusi P. Neli, and Ar- will be forcibly expelled to distances that gyroderma testiculare are among the best may be as much as a meter from the capsule. to obtain if available. In most capsules the seeds are attached to the capsule by long funiculi which anchor The Capsule and Seed Dispersal the seed and prevent it from a simply spill The capsules of the Aizoaciae include per- ing out of the capsule with overflowing

..e .B . . . e > ...... ^ . _~~~~~~~~~~~~~~~~~~~~~~~~...... -^:......

*' .... .,l | l I l I II~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~...... 222~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~.221......

t; z -$ r C F.i._.e I ^ > r S:~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~.....

Fig. 5, 6, 7. Progressive stages of opening of capsule of Fig. 11. Leaf top and miniature windows of Lithops ful. Glotiphyllum. viceps. Fig. 8. Side view of capsule shown in Fig. 7. Fig. 12. Miniature windows of illuminated. Fig. 9. Leaf top and window of Lithops bella. from beneath. Fig. 10. Window of Lithops bella illuminated from beneath.

The Xerophytic Mimicry Plants 203 water. Only by the relatively high impact of be buried an inch or so undergroundand a raindrop is the funiculus broken and the may receive light only through the window- seed catapulted out of the capsule. When ed leaf top which serves as a sort of "sky- the capsule dries out, the opening mechanism light."The leaf top may be a single window reverses itself and the valve lids close as in the case of ; it may be a to their original position. Repeated opening window with variouslyshaped opaque mark- and closing may take place in response to ings (Fig. 9) as in Lithops leslei; it may alternate wetting and drying. The closing consist of numerous irregularly shaped process is typically a gradual one, but under "panes;"or it may be a series of tiny round favorable conditions the capsule may open miniaturewindows (Figs. 11 and 12) as in completely in less than a minute, and the Lithops terricolor.The window is apparently -movement of the valves is quite apparent opaque in Lithops gracilidelineatabut still macroscopically. Any brief description of lets in sufficientdiffused light to supply the these capsules is necessarily quite incom- chlorophyllof the innertissues. plete, as they vary markedly from one genus The transparencyof the window is not Downloaded from http://online.ucpress.edu/abt/article-pdf/30/3/201/23957/4442008.pdf by guest on 02 October 2021 to another, although the basic mechanics of at all obvious externally, but if the top of operation is somewhat similar. Since germi- the window is cut off and held between the nation of the seed is only possible during observer and a light source, it becomes im- the infrequent periods of wet weather in mediately apparent (Figs. 10 and 12). It -the desert, the adaptive value of this mech- is also instructiveto slice off the window top anism which insures dispersal only during or to cut the plant longitudinallyto observe a hard rain becomes obvious. the bright green chlorophyll-containingtis- Capsules are produced readily on green- sue, which fills up the center of the leaf house grown plants and when mature, may beneath the window and furtherdiffuses the be removed and stored for future demon- intensesunlight. strations whenever desired. They are usually The plants are apparently able to with- retained in good condition on the plant for stand not only intense insolation but also at least a year. The open capsule is beautiful intense heat, as the leaf temperature of in its geometric perfection and never fails Lithops pseudotruncatellahas been reported to arouse student interest. as 56?C with the surroundingsoil temper- Adaptationto Insolation ature still higher. At the same time temper- Quite a few of the genera of Aizoaceae atures well below freezing are not uncom- have windowed leaves. This is a character- mon in the habitat of the same species. istic that is found widely distributed in xerophytic members of quite unrelated fami- Cultivation lies. An exercise in a recent labora- Cultivation of these plants is remarkably tory manual makes use of the variety of simple. They do extremely well and flower window formations found in spe- and set seed regularlyin a sunny greenhouse. cies (Liliaceae). Other examples of window They may be kept indoors a few inches formation are found in Peperomia dolabri- beneath 40 w. Gro-Lux fluorescent tubes forme (Piperaceae) and Kleinia herrianus and will grow well but will not flower. They (Compositae). also may be kept out of doors during the Among the genera having conspicuous summer if protected from rain by glass or windows are , , Opthal- plastic. mophyllum and Lithops, and it is in the latter The writer has grown them in various genus that they reach their greatest variety. soil formulationsand in both clay and plastic The paired leaves of the Lithops plant are pots. A mixture of two parts of sand with typically buried in the stony soil of their one part of loam and one part of leaf mold native desert with only the flattened top with sufficientlimestone to maintain a neu- at the surface of the ground. This habit may tral pH is quite satisfactory for clay pots. serve to cut down the rate of The amount of sand is increased and the and make the plant even less conspicuous. amount of leaf mold decreased for plastic Thus the chlorophyll-containing tissue may pots.

204 The American Biology Teacher, March, 1968 Watering must be done very judiciously if large numbers and great variety are de- and only on sunny days. The plant itself sired. should not be wet. The natural dry season for the plant is from June to September, General References and watering should be only sparing and Brown, N. E., A. Tischer, M. C. Karsten, E. J. La- Barre. 1931. Mesembryanthema. L. Reeve and once every few weeks during this time. Co. Ltd. Germinating in 5 days to 2 weeks, the Jump, John A. 1963. "Capsule Morphology and seed should be kept quite moist during the Seed Dispersal of Lapidaria margaretae."Cactus juvenile stage. A wide variety of species and Succulent Journal XXXV: 102-105. Nel, G. C. 1946. Lithops. Hortors Ltd. are available from collectors abroad. This Schwantes, G. 1957. Flowering stones and mid-day at present is the best way to obtain them flowers. Ernest Benn, Ltd. Downloaded from http://online.ucpress.edu/abt/article-pdf/30/3/201/23957/4442008.pdf by guest on 02 October 2021 Journal of Biological Education tory Animals Ltd., to the Subscription Man- Volume I, Number I of the quarterly Jour- ager: Dr. F. C. Chesterman, Imperial Cancer nal of Biological Education was published Research Fund, Burtonhole Lane, Mill Hill, jointly March 1967 by the Institute of Biology London, N.W.7, England. and the Academic Press. An annual subscrip- tion to this journal, which is intended to pro- Grant Data Quarterly vide a medium for exchange of new ideas A new journal devoted to information con- and information among teachers of biology cerning financial aid programs of all varieties at all levels, is $9.00. The Institute is located in the field of education. Subscription infor- 41 at Queen's Gate, London, S.W.7, England. mation may be obtained from Academic Media, 10835 Santa Monica Boulevard, Los Asian Regional Association Angeles, California 90025. for Biology Education Information about the Newsletter of the Correction Asian Regional Association for Biology Edu- The reviews of the two films SOS Gala- cation can be obtained from the Editor, pagos and Volcano Surtsey in the October, Dolores F. Hernandez, ARABE, Science 1967 issue of ABT were written by Fabian Education Center, University of the Philip- A. Glassman, Elmont Memorial High School, pines, Diliman, Quezon City, The Philippines. Long Island, New York. Mr. Glassman's name was inadvertently omitted as the reviewer. LaboratoryAnimals Laboratory Animals, Vol. 1 No. 1 of which Impactof Science on Society Impact of Science was published April 1967, is the official pub- on Society, the newly expanded quarterly lication of the Laboratory Animal Science journal of the United Nations Educational Association. The journal will publish research Scientific and Cultural Organization, contains papers, reviews, commentaries, and technical groundbreaking es- says on the social and other short communications on all as- consequences of science by social and natural pects of laboratory animal science. It is scientists. Single copies are 75 each. at hoped that the journal will be of particular Subscriptions $2.50 per year can be placed the interest to all scientists using laboratory ani- through UNESCO Publications Center, 317 East 34 mals for research and those responsible for Street, New York, New York, 10016. the supply, care, and maintenance of such animals. Initially there will be two issues each year, The Design,of Biological Laboratories one in April and one in October, comprising The Design of Biological Laboratoriesis one volume. The subscription rate is $7.50 available from the Institute of Biology, 41 per volume (two issues). Subscriptions Queen's Gate, London, S.W.7, England, for should be sent by check, payable to Labora- $3.00.

The Xerophytic Mimicry Plants 205