Torrey Pines Docent Society 2018, rev. 2019 Notes on the Wild The wild cucumber ( macrocarpa, meaning a bitter big fruit) is an attention grabbing . After a long dry season, this plant is among the very first to grow back quickly after light rains in late fall. The following spring, the plant produces large, prickly fruits that are a good conversation piece. These notes expand on the Margaret Fillius plant highlights column in the February 2016 issue of the Torreyana. In the latter half, the notes will cover the fish-stunning experiment led by Christina Bjenning in the November 2005 issue of Torreyana.

Key points: • The wild cucumber is well adapted to the short, wet winter in the Mediterranean climate. With food stored in the tuber (the storage root), it can start growing quickly after the onset of a rainy season, and the plant returns to a dormant state underground soon after. In fact, the plant spends most of the year underground. • The plant has separate male and female flowers. The male flowers are the smaller ones clustered along a stalk. The female flowers appear by themselves, and even when very young, one can observe a small swelling, the , behind the flower. • The seeds are huge, as one might guess from the size of the compartments in a dried fruit. The seed germination is adapted to self-planting a tuber deep underground without sunlight. Thus a large food reserve is needed. • The seed dispersal is by rodents with underground burrows. By being hidden underground, the seeds are well protected from wildfires in the dry season. • The seed pods split by uneven drying of the skin, but the molecular biology underlying the drying is complicated. • A tendril tightens its grip by coiling. The coiling is attained by uneven contraction within a tendril, and the contraction is generated by a lignified cell layer. One often sees two coils on a tendril—a tendril starts coiling up separately from each respective end. Charles Darwin had studied the phenomenon in detail. • The entire plant is bitter because it contains saponins, a soapy substance. Chemically, the saponins in the wild cucumber contain cucurbitacins, which can have various medicinal properties. (But too much of these chemicals is toxic.) • Native American groups along the coast had many uses for in the same genus as the wild cucumber. Notable uses are in stunning fish and body or face painting using roasted seeds. A really interesting use is in the treatment of men’s hair loss.

1 What is so unique about the wild cucumber? Charles Darwin studied a wild cucumber, even though it is not exactly the same species as what we have locally. , the renowned American botanist, mailed Darwin some seeds of lobata, which is found east of California, and also called the wild cucumber. Indeed, E. lobata, now classified in its own monotypic genus, shares many general characteristics with our local species, . Darwin studied the E. lobata, and wrote about the unique germination features and the intriguing tendril coiling. The wild cucumber is a geophyte—a plant that spends most of its time underground, and these plants often have an underground storage organ. With the wild cucumber, the aboveground structures die off, and the plant stays as an underground tuber most of the year. However, it can sprout the quickly at the onset of a rainy season in late fall or early winter. Pretty white flowers and interesting spiky fruits develop quickly afterward.

General characteristics of the wild cucumber The common name “wild cucumber” is used by various sources for several related Marah species, not to mention also for Echinocystis lobata. So is the other common name, manroot, for the enormous tuber or storage root. A large one can weigh well over 200 pounds. Marah macrocarpa, the common species in San Diego, has other common names, including Cucamonga manroot, the Chilicothe, and the bigroot. The genus name Marah means bitter, a reference to the bitter waters of a fountain in Marah in the Bible. The species name macrocarpa means large fruit. So what we have is a bitter big fruit, but the entire plant is bitter. All parts of the plant have various quantities of a bitter chemical (more on this later). The Marah genus, native to Western North America, is in the gourd family, . Plants in this family that are familiar to us include squash, pumpkin, zucchini, watermelon, and of course, the common cucumber (Cucumis sativus). Most of the gourd plants are vines. They are either monoecious or dioecious, meaning that they have separate male and female flowers either on the same plant or on different plants. Their flowers are funnel-shaped with generally 5 petals. The female flowers have inferior ovaries, and the fused carpels are separated by septa into compartments (locules). There are at least five species of Marah in California. The most notable and studied ones are Marah oregana and . Their natural ranges are north of San Diego County, especially M. oregana as suggested by its species name. The range of Marah macrocarpa is concentrated in Southern California, and this species is particularly well adapted to a long, dry summer. Where ranges of different Marah species overlap, they can hybridize. The vines of Marah macrocarpa can reach well over 20 feet (6 m). Spaced intermittently along a stem are nodes. At each node one finds the of a leaf, a short pedicel of a single female flower, a longer peduncle leading to a raceme of male flowers,

2 and a small branch leading toward a tendril. If this tendril-bearing branch keeps growing long enough in search of an anchor, it may small leaves and also branch off to make multiple tendrils. The number of male flowers in an inflorescence increases with time into the season. There may be three to five at the beginning, and eventually increasing to well over a dozen. The Marah species is monoecious. Both the male and female flowers have five white petals that together take a shallow cup shape (cupulate) and the appearance of a starfish. The petals bear white, soft hairs (pubescence). At the center of the smaller male (staminate) flowers, about 2/3-inch (17 mm) in diameter, is a ring of fuzzy yellow anthers. The female (pistillate) flower, about 1¼-inch (32 mm) in diameter, has a yellowish, cushion-like at the top of a compound pistil from fused carpels. A small, spiky inferior ovary is already evident when the flower is very young. The sepals are fused in both the male and female flowers. (See photos in Fillius 4th edition, p. 167.) The wild cucumber is pollinated by , but the plant is self-fertile, meaning that pollens from the male flowers can fertilize the female flowers on the same plant. The leaves are palmately lobed with generally five irregular lobes, and the two lobes near the base have smaller sub-lobes. The main veins are also palmate, but the secondary venation is cross-venulate within a lobe. The leaves on a given plant can exhibit large variability in shape and size. The fruit is a pepo. Even though it is not as fleshy as other gourd plants, the fruit is made from a fused carpel and has a tough skin or rind. The fruit is oblong, and easily over 4 inches (100 mm) long and 3.5 inches (90 mm) in diameter. The fruit capsule spines that are soft when young, but they stiffen up quickly. The spines are of uneven lengths, with short bristles (spinules) interspersed among some long ones over an inch in length. Inside the fruit are four compartments separated by septa. Each chamber can hold as many as six seeds. The number varies. As many as 20 seeds from one fruit have been observed. The oblong-elliptic seeds are hard, and large, easily 0.6 inch (15 mm) in length. The seed is olive green or dark tan, and turns to a dark gray with time after the fruit has split. The Western scrub jay is known to eat the seeds, but the seed dispersal is carried out mainly by burrow-dwelling rodents such as deer mice, kangaroo rats, and especially the bigger ground squirrels. In an experiment by Borchert (2006), he found that about 90% of the seeds were moved to underground burrows. Because the seeds are below ground, they are protected from wildfires, and this way, the wild cucumber is well adapted to the fire ecology of the habitat.

3 Fig. 1. Germination photos 12 and 13 of (the old synonym of Marah oregana) from Schlising (1969). Photo 12 on the left shows a seed (S) germinating several inches underground. The petiole tube (P) grows from the seed and extends deeper into the soil, being led by the hypocotyl (H) and the radicle (R). Photo 13 on the right shows that roughly six inches farther down from the seed, the root forms a small tuber (T). From the tuber, the epicotyl (E) grows back up in the petiole tube and eventually breaks through and continues toward the soil surface.

Fig. 2. Epicotyl growth photos 10 and 11 of Marah oreganus from Schlising (1969). Photo 10 on the left shows a young epicotyl (E) in the middle of the petiole tube, the radicle (R) below it, and in between them a developing tuber. (The labels E and R are not very clear in this old photo.) Photo 11 on the right shows an older epicotyl continuing its growth up the petiole tube, above a slightly bigger tuber above the radicle.

4 The wild cucumber has an unusual hypogeal germination In hypogeal, or underground, germination, the seed stays underground, and the cotyledons remain non-photosynthetic. The common pattern is that an epicotyl and a hypocotyl grow from the seed. The epicotyl eventually bears the young shoot above ground, while the hypocotyl extends to become the radicle, the embryonic root. The hypogeal germination of the wild cucumber, or Marah sp., is rather unusual, and appears to be an adaptation to establish the important tuber underground. In addition, a seed sown on the surface does not germinate successfully even when being watered well. The seed has to be planted deeper as in a burrow. Soon after the late fall rains in early December, the first structure that forms is a hollow tube, called the petiole tube, that evolves from the base of the cotyledons and led by the hypocotyl (Figure 1). The petiole tube extends about six inches deeper into the soil. Roughly 10 inches below the soil surface, the hypocotyl begins to grow laterally to form a small tuber. Thus the tuber is well placed underneath the seed with a self-planting mechanism. While the tuber is being formed, the radicle grows from its underside, and the epicotyl emerges from the upper side and grows back up the petiole tube (Figure 2). Eventually, the shoot breaks through the tube and continues toward the surface to produce a young shoot with leaves, usually by early March. This young dies back quickly by May as the dry season approaches, and stays dormant until the next winter rain. The second year shoot grows above ground again in January to form flowering plants.

Why are the seeds so large? From the petiole tube to the small tuber and the epicotyl, there are not yet any green leaflets above ground. Needless to say that the seed has to be large enough to drive the germination. The entire process has to be fueled by energy stored as food granules in the seed endosperm. The large seeds are among many adaptations of the wild cucumber to a short, wet winter typical of a Mediterranean climate, and wildfires in the chaparral habitat. As explained above, a large seed is needed to have a food reserve, and by self-planting a tuber deeper, the tuber is placed in a depth with higher soil moisture. The tuber, as a storage root, enables the second year seedling and matured to sprout quickly at the onset of a rainy season. During the dry, fire-prone season, the underground tuber and seeds cached in a rodent burrow, if not eaten yet, are protected from wildfire.

5 Fig. 3. Illustration of a coiled tendril from Darwin (1875). He observed that the helical coils rotate in opposite directions and meet near the middle of the tendril. This location and the shape of the coils vary with each tendril.

How do the tendrils make the spiral coils? Charles Darwin had studied the coiling of tendrils as part of his research of climbing plants, and he made many key observations. The mechanism behind the coiling, however, was not known for a long time. Now we know that the coiling is a result of, in fancy wording, asymmetric contraction of a bilayer. In simpler terms, uneven shrinkage can cause a fiber to curl up and form a coil. Initially, a tendril growing from a branch of the vine is linear; it is like a thick piece of hair, and it can be as long as five inches or more. Once its tactile cells detect a solid foothold, the tendril tip will wrap around it (mechanism likely the same as what is described below) and secure an anchor. The tendril then shortens the distance between the branch and the anchor, and tightens up the grip. In the process, the tendril forms a helical or corkscrew-like coil. Furthermore, the coil is often made up of two halves that rotate in opposite directions (Figure 3). Thus the tendril shortens by coiling. The coiling is a result of asymmetric contraction of the tendril, which has turned into a bilayer structure as a result of tissue morphosis. After a tendril has clasped an anchor, it starts to transform some cells into a thin, stiff layer near one side (Figure 4). The cell wall of this stiffened layer is reinforced by lignification, the deposition of lignin. Darwin had made the observation that coiled tendrils were stronger and more durable, and inferred that the internal tissue must have been changed. The lignified cell layer essentially inserts a shank in the tendril, effectively making a bilayer structure. More importantly, lignin is hydrophobic. The lignification expels water locally and leads to a slight contraction of a lignified cell. Altogether, this stronger lignified cell layer is slightly shorter than the tendril, and its formation forces the side where it is on to contract. The uneven contraction leads to coiling of the tendril. The contraction layer (i.e., the side with the lignified layer) forms the inner side of a helical coil, with the softer part on the outside. The lignified cells are called gelatinous fiber or g-fiber cells, and they are the same as those that are made in reaction wood that is typically formed on leaning stems and branches under gravitational or bending stress. When a stem makes lignified cells to

6 resist bending, the reinforced layer is called compression wood.

Fig. 4. Selected images from Gerbode (2012) on the formation of lignified fiber cells. (B) An uncoiled tendril has no lignified fibers; (E) presence of a thin band of lignified fiber cells located near one side of the fiber, which will become the inner side of a coiled fiber; (G) higher magnified view of the lignified fiber cells with thick, reinforced cell walls. Scale bars in (B) 500 μm, (E) 100 μm, and (G) 10 μm.

If one person twists continuously, say, one end of a rope in one direction, the torque will spin the other end of the rope. To prevent that from happening, another person needs to hold the other end and twist the rope in the opposite direction (from the perspective of the first person) to counteract the torque from the other end. This is what happens when a tendril shortens itself between two strong, stable points—a branch and an anchor point on another plant. The tendril shortening generates from each end a helical coil. Looking from one end of a tendril, the two coils rotate in opposite directions, but that is because from each respective end, the tendril tries to coil the same way, say, both clockwise from each end. The double coils meet at a neutral point called the perversion near the middle of the tendril. In canceling the opposing torques, the double coil is also called a twistless spring. The actual shape of the coiling varies. The occurrence of two perversions is common, especially with a longer tendril. There is no rule that dictates the initial direction of coiling from one end. If a coil happens to rotate in the same direction as the other end, this will lead to a middle segment that coils in the opposite direction as from both ends. Furthermore, coiling variation also arises from uneven formation of the lignified cell layer.

How does the fruit pop open? When the wild cucumber fruit splits, it pops and appears as if it explodes with a gas inside. Nonetheless, there is no gas and the underlying mechanism is complicated. The splitting of the capsule is due to uneven shrinkage of its walls. We went through similar learning process with the peat moss, genus Sphagnum. Until we have better understanding on how a moss spore capsule (sporangium) splits open, it was thought that the capsule explodes like an air gun.

7 Dehiscence, the splitting of a plant structure, can occur with sporangia in moss, anthers of some flowers, and in our most common encounter, ripe fruits ready for seed dispersal. The forces that enable dehiscence are most often due to stresses generated by uneven (aka differential) drying of different parts of a fruit. The fruit then splits along lines of weakness. The force unleashed from relieving the pent-up stress can be so powerful that a fruit may appear to explode or squirt. As simple as drying sounds, dehiscence is tightly orchestrated by over half a dozen genes, and occurs within a well defined dehiscent zone. Much of the understanding of dehiscence came from studies of the mustard arabidopsis (Arabidopsis thaliana). As the wild cucumber fruit approaches maturity, the skin (epicarp) is stretched tightly over the white pulp (mesocarp), and the apex (the distal end) begins to dry out, eventually forming a brown cap. The dehiscence zone is just a few cells wide around the cap circumference. When the fruit finally splits, the skin snaps back quickly, and rolls up toward the base of the fruit. The motion can be violent enough to make a popping sound and shake the seeds loose from the fruit. Afterward, the entire fruit dries out. Nonetheless the pulp stays rigid; the fruit capsule does not become flaccid, as would be the case if the fruit were exploded by gas accumulation (or an air gun).

A B

Fig. 5. The chemical structures of (A) Cucurbitacin B, which has been isolated from Marah species, and (B) finasteride, a drug used in the treatment of male-pattern baldness. Both molecules are built on similar looking four-ring structures which roughly resemble the one in sterols.

Wild cucumber contains cucurbitacins We should first look into the important biochemicals in the plant before covering its medicinal uses. Plants in the gourd family contain cucurbitacins, an important class of compounds named after the family. Of course, some plants make more of these chemicals than others. These compounds taste bitter and work as a deterrent to foraging herbivores. Chemically, cucurbitacins are terpenoids. More specifically, they are tetracyclic triterpenoids, which are four-ring compounds derived from six isoprene (terpene) units. The common ones found in plants are named Cucurbitacin A, Cucurbitacin B, and so forth to Cucurbitacin T. Cucurbitacins are also classified as steroids because they are built on a four-ring structure (Figure 5A) that is also the building block of steroids. In plants, cucurbitacins are often chemically bonded to a sugar chain to form cucurbitane

8 glycosides. A common name for glycosides of triterpenoids in general is saponins. Saponins are amphiphilic (aka amphipathic) compounds with the lipophilic triterpenoid part and the hydrophilic sugar chain, and so they have soap-like foaming properties. Many saponins can lyse red blood cells (haemolytic), and are toxic to cold-blooded animals, especially fish. In terms of pharmacological activities, the steroidal cucurbitacins can be anti- inflammatory and analgesic (very similar to how cortisone works). The action is by inhibiting the enzyme cyclooxygenase 2 (COX-2), and thus preventing the formation of prostaglandins, which trigger both pain neurosensors and downstream inflammatory responses. The root of the wild cucumber is a strong laxative, possibly a result of the soapy property of saponins. Ribosome-inactivating proteins (RIPs) have been isolated from Marah oregana. RIPs are toxins that inhibit protein synthesis, and likely are made as part of a plant defense against microorganisms. They probably are responsible for imparting anti-fungal properties to the plant, especially to the tuber buried in moist soil.

Ethnobotany of the wild cucumber The wild cucumber is a good cautionary tale on how we must be careful with sources of ethnobotany information. Many cited uses of the wild cucumber by specifically the Kumeyaay in stunning fish are traced back to the Wikipedia page on Marah fabaceus (the old synonym of Marah fabacea), which references the experiment led by then docent Christina Bjenning in the November 2005 issue of Torreyana. Bjenning and her team were very clear that they were interested in how “native peoples” managed to stun fish, and that they found an old paper that identified a saponin in Marah fabaceus, which grows only north of San Diego. Nonetheless, this particular Wikipedia contributor made a huge leap of faith in addition to making other factual errors. Martin (2009) provided a telling review. He looked into the uses of different Marah species by various coastal Californian native groups. He also tried to tell apart the prehistoric uses from the influences of the missionaries. He noted that carbonized seed coat fragments were found in many archaeological sites, an indication that the plant was widely used in various ways by indigenous groups. His summary of the usages is reproduced as Table 1 below. A notable pattern is that each individual group has only a few uses of the plant, and the uses vary from group to group. If taken all together without the context of geographic location, it would appear that the plant was once used for almost anything by one group. In this regard, an aggregate of all the uses may include: • As an anti-inflammatory and analgesic agent to treat conditions including wounds, sores, toothache, and hemorrhoid • As an anti-fungal agent • As a laxative

9 • Fish poison • Treat hair loss • Seeds for gaming pieces and making jewelry; roasted seeds for body paint

The first few uses from anti-inflammatory agent to a fish poison rely on the properties of cucurbitacins or saponins. The root is the part that is used mainly as a laxative and for making soap and fish poison. The content of cucurbitacins is higher in the roots than in the leaves and seeds. This in fact was the result of the experiment led by Bjenning. The need of a laxative could be tied to the consumption of acorn, a common staple food. Acorn contains a high content of tannic acid, which can inhibit digestive enzymes and also binding protein, making it indigestible. That is why acorn mush has to be leached with water before cooking. However, if the leaching is not thorough enough, the tannic acid residue could lead to constipation. While the root may be more effective as a purgative, roasted seeds were also used, especially with young children. What is interesting is how the plant was used to prevent men’s hair loss, and it was a common usage among many native groups. Male-pattern hair loss (androgenetic alopecia) is caused by hair follicles being over-sensitive to 5α-dihydrotestosterone (DHT). DHT is produced from testosterone by an enzyme (5-α-reductase). For some reason, the scalp can be rich in testosterone. Cucurbitacins can inhibit the enzyme activity and prevent the formation of DHT in the scalp. Cucurbitacins contain a tetracyclic triterpenoid structure (Fig 5A) very similar to that in testosterone, and thus it is likely that cucurbitacins work by competing for the enzyme (i.e., via competitive inhibition) in cutting down the formation of DHT. The native groups made a ground paste from the seeds or they extracted the seed oil, and they rubbed the substance into the scalp. In the modern age, we can buy a hair loss drug made of the chemical finasteride (Fig 5B). Note how finasteride, considered an antiandrogen, also contains a very similar tetracyclic triterpenoid structure.

How does saponin kill fish? There are no detailed mechanistic studies, and thus there is no definitive answer. The general consensus is that saponins can lyse red blood cells, which are important in carrying oxygen. The use of saponins in Asian shrimp farms may provide us some insight. Shrimp farmers in Thailand and Malaysia prepare a pond by first filling it with a foot or so of water and then adding tea seed extract to kill any predatory fish. The extract of tea seeds (Camellia sp.) contains saponins. Application of about 15 ppm of saponin for 6 hours is sufficient to kill most fish, and to leave the extract in the pond longer, even just 1 ppm can kill most of the fish. One parts per million (1 ppm) is like one teaspoon in a million, or about 84 kegs of beer, which is a tiny quantity. (Because fish can be killed by such a minute quantity of saponin, it is generally not advised to use soap to clean aquariums.)

10 After the tea seed extract treatment at such low quantities, any residual saponin does not harm the shrimp. The lethal concentrations of saponin required to kill crustaceans (shrimps and crabs) are at least ten times higher. Crustaceans have gills too, but they do not use hemoglobin in their blood cells to carry oxygen. Crustaceans use instead free- floating hemocyanin in their blood to carry oxygen. (Hemocyanin is a molecule that contains copper and this is why the blood of crustaceans is blue.) Hence with shrimp farm practice as a hint, it is unlikely that saponins kill fish by damaging the gill. The lysing of red blood cells is the more probable cause. And because crustaceans eventually can still be killed with a high enough concentration, saponins may also interfere with the oxygen-binding capability of hemoglobin and hemocyanin.

Table 1. The varied uses of the wild cucumber and its related species by different Native American groups from Martin (2009). People Uses of Marah macrocarpa Cahuilla Anti-fungal agent with juice extract from the fruit rind Treat hair loss with oil extracted from the seeds Chumash Strung seeds as beads as jewelry Use the seeds as gaming pieces Birthing aid, using a drink made of toasted, mashed seeds Purgative, with black powder from charred seeds Treat hair loss with oil extracted from roasted seeds Body paint and ritual with oil extracted from roasted seeds Gabrielino Use toasted seeds mixed with ground stone for wounds, anti- inflammatory, urinary aid, treat cataracts, induce menstruation Treat hair loss with charred and ground seeds Kumeyaay Body paint and ritual with charred, ground seeds (Diegueño) Treat hemorrhoids with boiled leaves (per Delfina Cuero) Luiseño Purgative, using the root Treat hair loss with roasted, mashed seeds Body and rock paint with roasted, mashed seeds Anti-inflammatory, applying oil extracted from seeds to swellings

11 Table 1, continued. People Uses of Marah fabaceus (California manroot, Bigroot) Kashaya Pomo Treat hair loss with the root, pounded and mixed with pepper nuts and skunk grease Mashed root as fish poison (Southwestern Pomo used the seeds) Yuki Treat toothache with pieces of dried root in the cavity

Uses of Marah horridus (Sierra manroot) Kawaiisu Treat skin conditions with roasted and mashed seeds Treat hair loss with roasted and mashed seeds Tubatulabal Rub burned seeds on newborn as birth ritual

Uses of Marah oregonus (Oregon manroot, Coastal manroot) Chehalis Treat lymph node swelling with burned and powdered root Costanoan Use the root as soap Treat skin conditions with mashed seeds Karok Treat skin conditions with a poultice from the root Oregon Paiutes Use a decoction of the root as eye medicine Pomo Suicide and euthanasia Fish poison using the root Treat rheumatic conditions with both the seed and root Treat venereal disease with the seed Purgative using the root Sinkyone Use roasted seed for food Squaxin Analgesic using mashed stems Yurok Use the shoots with Polypodium sp. to make a tea Fruits as toys

Annotated Bibliography ● Related to the germination characteristics of the wild cucumber

Borchert, M. (2006). Seed fate of Marah macrocarpus (Cucurbitaceae) following fire: do seedlings recruit from rodent burrows? Ecological Research 21, 641–650. – Extending the work of Robert Schlising by a ranger at a reserve in Ojai Valley, Ventura County. He studied how the seeds were dispersed by rodents and the germination process. He considered the seeds of the wild cucumber a pyrogenic flowering geophyte.

12 Dathan, A.S.R., and Singh, D. (1971). Morphology and embryology of Marah macrocarpa Greene. Proceedings of the Indian Academy of Sciences Section B 73, 241–250. – An old study but provided extremely detailed observations on the fertilization and development of the embryo and the seed.

Schlising, R.A. (1969). Seedling Morphology in Marah (Cucurbitaceae) Related to the Californian Mediterranean Climate, American Journal of Botany 56, 552-560. – Among the most authoritative studies of the plant. The paper is based on his thesis work. Has nice photographs and mentioned the writings of Asa Gray and Darwin.

Stocking, K.M. (October, 1955). Some Taxonomic and Ecological Considerations of the Genus Marah (Cucurbitaceae). Madroño 13, 113-137. – Studied mainly Marah oreganus and Marah fabaceus, and observed the hypogeal germination and other characteristics that are confirmed by subsequent studies. Also mentioned that because of its purgative properties, the tuber of M. fabaceus was used in Stroughton's Bitters as a laxative (no longer the case with the “modern” version).

● Related to the tendril coiling in the wild cucumber

Darwin, Charles (1875). The Movements and Habits of Climbing Plants (London: John Murray). Available from Project Gutenberg, http://www.gutenberg.org/ebooks/2485 – Based on his 1865 essay, considered the first edition and which appeared in the ninth volume of the Journal of the Linnean Society, with corrections, additions, and illustrations by his son, George Darwin. Darwin made some extremely thorough, detailed, and insightful observations on a large of climbing plants. The research literature has a reference to “Darwin's perversion,” which was used in acknowledgment to his early observations. Perversion is a term coined by mathematicians in the study of topology in the inversion of handedness (chirality). The first use of “tendril perversion” was probably by the mathematicians Alain Goriely and Michael Tabor in their 1998 analysis published in the Physical Review Letters.

Gerbode, S.J., Puzey, J.R., McCormick, A.G., and Mahadevan L. (2012). How the Cucumber Tendril Coils and Overwinds, Science 337, 1087-1091. – Probably the first study that unravels the mystery in tendril coiling. In addition to studying the cucumber tendril, the research team also made a biomimetic model using silicon rubber layers to reproduce the phenomenon, including overwinding. The two species used in this study are Cucumis sativus, the common cucumber, and Echinocystis lobata, also called the wild cucumber, found east of the West Coast. Sharon Gerbode and colleagues also made a video. Search YouTube with “cucumber tendril” and find the one from Science.

Sandrine I., and Silk, W.K. (2009). Moving with Climbing Plants from Charles Darwin’s Time into the 21st Century. American Journal of Botany 96: 1205–1221. – Darwin bicentennial special invited paper; extremely thorough on the biology of climbing plants.

● Related to fruit dehiscence

Duckett, J.G., Pressel, S., P’ng, K.M.Y., and Renzaglia, K.S. (2009). Exploding a myth: the capsule dehiscence mechanism and the function of pseudostomata in Sphagnum, New Phytologist 183, 1053–1063.

13 – The study that dispels the myth of the air-gun explosion of spore discharge in Sphagnum.

Ferrándiz, C. (2012). Regulation of fruit dehiscence in Arabidopsis, Journal of Experimental Botany 53, 2031–2038. – A review on the biochemistry and molecular mechanism of fruit dehiscence in Arabidopsis. Some of the more notable dehiscence genes make transcription factors in the MADS-box gene family that is important in many developmental processes, and they include genes with names such as SHATTERPROOF1 (SHP1) and FRUITFULL (FUL).

● Related to the ethnobotany of the wild cucumber

Martin, S.L. (2009). The Use of Marah Macrocarpus by the Prehistoric Indians of Coastal Southern California. Journal of Ethnobiology 29, 77–93. – A thorough review of prehistoric uses, including differentiating uses by different native groups and different Marah species, by (not the comedian) Steve Martin when he was at the UCLA Cotsen Institute of Archaeology.

Rusting, R.L. (June 2001). Hair: Why It Grows Why It Stops. Scientific American 284, 70–79. – Covered the biology of hair growth with a sidebar on drugs that can prevent pattern hair loss (androgenetic alopecia), including finasteride, which is marketed as Propecia.

● Related to fish poisons

Cannon, J.G., Burton, R.A., Wood, S.G., and Owen, N.L. (2004). Naturally Occurring Fish Poisons from Plants. Journal of Chemical Education 81, 1457–1461. – A review of fish poisons (piscicides) and their mechanism of action. Even though triterpenoid saponins are common fish poisons, there are still uncertainties on how these compounds actually work, especially as hemolytic agents.

Terazaki, M., Tharnbuppa, P., and Nakayama, Y. (1980). Eradication of predatory fishes in shrimp farms by utilization of Thai tea seed. Aquaculture 19, 235-242. – An old but detailed study of the effect of crude saponin extracts on fish and crustaceans in shrimp farms.

Chen, J., Chen, K., and Chen, J. (1996). Effects of saponin on survival, growth, molting and feeding of Penaeus japonicus juveniles. Aquaculture 144, 165-175. – A follow up to the work of Terazaki et al. with the focus on the shrimp.

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