Self-Guiding Tour of the Biology Greenhouse

Warren G. Abrahamson



Desert

Wetlands

Tropical and Temperate Forests




Biology's rooftop greenhouses are used for both teaching and research. Room 409 houses the museum collection, while room 410 is used for research projects. All greenhouse preparations are conducted in rooms 402, 403, and 404.

PLEASE NOTE:
1. Many of the plants overhang the aisles between greenhouse benches. Certain plants are damaged by handling. Also, you can be hurt as well, particularly by the spines or thorns on many plants. So it is a good idea to look, but be careful if you touch.
2. How to read pot labels: Labels usually bear the Latin binomial (genus and species). The labels also should have the family name (sometimes on the back). According to the rules of nomenclature, family names end in an aceae (the mustard family is Brassacaceae, for example). However, four older traditional family names persist that do not end in aceae (e.g., Leguminosae for the bean family, Compositae for the sunflower family). We are also actively adding common names to the labels.

The plants of the Bucknell greenhouse are more or less grouped by ecosystems including desert, freshwater wetlands (e.g., ponds and bogs), and tropical and temperate forests.

DESERT.

This portion of the greenhouse has a somewhat warmer temperature and is more sunny than the other portions of the museum greenhouse.

Xeric (dry) Environments. These are places where water is scarce. This includes not only deserts, but saline habitats where the high salt content of soils creates water stress, or habitats where the water may be frozen most of the year. Xeric environments may be very localized, such as in rock outcrops at high elevation where the sunlight is intense and water is scanty during the summer. Annual plants growing in xeric environments can avoid drought by completing their life cycles during the brief season when water may be available and then surviving the rest of the year as seeds. Perennial plants which can not avoid the drought in this way, they have evolved a variety of adaptations which allow them to withstand water scarcity. Such plants are known as xerophytes. The following is a partial list of the structural adaptations (modifications that increase fitness) shown by xeric plants. There are interesting physiological adaptations as well including CAM and C4 photosynthetic pathways but we will concentrate on the features you can see in the Bucknell greenhouse.

Stem succulence. Stems that are fleshy and water-storing are referred to as "succulent". Such plants often have no leaves and the stem does all the photosynthesis.

Ribs. Prominent vertical ribs on succulent stems allow them to expand or contract like an accordion as the water content increases or decreases.

Leaf succulence. Plants often store water in fleshy leaves, in which case the stem may be much reduced in size.

Hairiness. A dense covering of hair reflects sunlight, keeping plants cooler - which cuts down water loss. It also reduces water loss by preventing wind from sweeping away the layer of water-saturated air that exists near stomatal openings.

Glaucousness. This term refers to the whitish bloom one sees on many plants. The bloom consists of a fine layer of wax particles that reflects sunlight.

Spines and thorns. These are modified leaves and stems, respectively, and almost certainly evolved in response to predation by thirsty desert animals.

Look for: PLANTS WITH XERIC CHARACTERISTICS AND EXAMPLES OF CONVERGENT EVOLUTION.

Notice that many of the plants which you might be tempted to call cacti are not in that family (Cactaceae), they are actually genetically unrelated. We have examples of many plant families which show a cactus-like form (read pot labels, remembering that family names end aceae). Compare the large Euphorbia lactea (dragon bones--to the left) or Euphorbia trigona with Idria columnaris (boojum-tree--to the right) and with Cereus or Pereskia (--to the left) cacti. The former evolved in the Old-World deserts while the latter evolved in New-World deserts. While genetically unrelated, these families exhibit convergent evolution in their adaptations to similar xeric conditions. Other examples of convergent evolution in animals include fish and whales.

Look for: "WINDOW PLANTS" or "STONE PLANTS" (on the table to the right).

One way to escape the killing heat of the desert is to go underground, which is what many of the animals do. Window plants (Lithops) are entirely subterranean except the nearly transparent leaf tips which are exposed at the soil surface. These areas of transparency allow light to penetrate to the interior and strike the photosynthetic tissue. But most of the plant is not exposed to the heating effects of high light intensity and to the drying effects of desert air. There are no stomata in the windows, so little water is lost. Growth is slow, but it does occur...so how do these plants remain subterranean? They have contactile roots which continually pull the plants deeper into the ground as the stem elongates. The leaf tips look like stones and so these plants are also known as "stone" plants. They are native to the hottest deserts of southern Africa.

Look for: CRASSULACEAE (a family which has many leaf succulents--scattered throughout the desert area but be sure to see the large Jade tree on the right near the end of the desert section).

This family is interesting for a number of reasons (e.g., presence of the CAM photosynthetic metabolic pathway--a pathway that is very water conservative) One thing you will notice on many species is the apparent absence of a stem. It is there, but stem regions between leaves (internodes) are so short that they can hardly be seen. This produces a "rosette" form.

Study several rosette plants. You should be able to see rather easily that the leaves are arranged so that two sets of spirals can be seen, a clockwise set and a counter-clockwise set. If you were to count the number of spirals in each set, only certain numbers would turn up. They are the numbers in a Fibonacci sequence (1,1,2,3,5,8,13,21,34,55, etc.). Notice that each number is the sum of the two preceding it in the sequence. Normally the pattern cannot be seen because of stem elongation and stem twisting, but it is very obvious in something like a giant sunflower where the seeds are packed into beautiful Fibonacci spirals, or it can easily be seen in a pine cone. In the Compositae (sunflower) family, the disk flowers and seeds are arrranged in two sets of logarithmic spirals, one clockwise, the other anticlockwise which produce arms that radiate from the flower's center.

It is apparent that the shoot tip, where leaves and other structures are born, operates with incredible mathematical precision. Scientists studying these patterns hope to understand the biochemical and physical mechanisms underlying form, but it is a very difficult problem and we are far from understanding it.

Look for: POLLINATION INVOLVING CARRION FLIES AND STAR FLOWERS

If you are in luck, Stapelia spp. (Asclepiadaceae, a family which includes milkweeds) will be in flower. If not, you will have to rely on the drawing in the left hand-margin. The flowers are purplish-red, sort of meat-colored, and you will discover, if it is ripe, that it also smells like rotting meat - more specifically, a long-dead animal. When the flower is mature, it emits foul-smelling gases that attract flies and other carrion-loving organisms which serve as pollinators. They come in search of carrion and are soon "dusted" with pollen as they lay their eggs. They leave to fly to another such plant where, they may be fooled again - but this time their visit will carry out cross pollination because they bring a load of pollen. The larvae that hatch from the eggs die as the flower provides no nourishment.

Aristolochia spp. (Aristolochiaceae, a family which includes wild ginger). The unusual flowers give Aristolochia species their common name, "Dutchman's pipe". Note their color; these flowers operate much like the plant described above - attracting flies and gnats, by producing a foul odor.

Look for: PLANTS IN FLOWER.

The outstanding characteristic of angiosperms or flowering plants is the flower. Most flowers contain two sets of sterile appendages, the sepals and petals, that are attached to the receptacle below the fertile parts of the flower, the stamens and carpels. Given the basic structure of the flower, many variations exist in sex, number of floral parts, arrangement of parts, and symmetry. The Bucknell collection has flowers of many forms that clearly illustrate the great diversity in floral types.

This floral variation relates to the mode of pollination of a given flower. Some flowers are pollinated passively, by the action of the wind or water. The stigma catches pollen grains as they contact its surface. These flowers are not showy as no advertisement of the flowers presence is necessary (e.g., ragweed).

Many flowering plants, however, produce conspicuous, showy blossoms that attract insects and other animals (e.g., goldenrod). These flowers actually direct the activities of the floral visitor so that a high frequency of cross-pollination of the plants will result. In a sense, the angiosperms have transcended their rooted condition and become just as motile, reproductively, as the higher animals.

How could this come about? The more attractive flowers were to early insects (e.g., beetles), the more frequently they would be visited, and the more seeds they would produce. Any chance mutations that made the visits more frequent or more efficient offered an immediate selective advantage. By the beginning of the Cenozoic era (65 million years age), bees, wasps, butterflies, and moths had made their evolutionary debut. The rise of these long-tongued insects, for which flowers are often the only source of nutrition, was a direct result of angiosperm evolution. In turn, insects profoundly influenced the evolutionary course of the angiosperms and contributed greatly to their diversification. This type of evolutionary interaction has been referred to as diffuse coevolution.

Try to predict what the pollinators of the flowers you see might be.

Bee flowers have odors and brightly colored petals, usually blue or yellow. There are often distinctive color patterns (e.g., lines that radiate, circles of varying colors) that make recognition of specific species easier for the bees. For example, many flowers use patterns reflective in the ultraviolet region (unfortunately, our eyes cannot detect ultraviolet). which produce "nectar guides" that aid the bees in locating nectar or pollen resources. As bees collect nectar and/or pollen, they often show a high degree of constancy for certain plant species. This constancy facilitates the efficient handling of flowers but it also increases the likelihood of cross pollination within a plant species. There are at least 20,000 species of bees and about 25,000 species of orchids, and many have an obligatory one-on-one relationship.

Butterfly flowers are also brightly colored and produce odors (although a different range of odors than are found in bee-pollinated flowers). They may be blue and yellow, but many are red or orange. Although their shapes are various, a flat-topped cluster of small flowers is almost invariably a butterfly flower. The flat cluster provides a landing platform. These platforms are displayed to perfection on Asclepias tuberosa, a local plant known as "butterfly weed". Butterfly weed is often covered with butterflies in summer. Flowers with long corolla (i.e., all petals taken together) tubes are frequently butterfly- or moth-flowers since these insects have a long proboscis (i.e., tongue) which they can unroll like a New Year's Eve horn to reach the nectaries at the base of the flower. Moth flowers are open at night and are most commonly white - a color easily seen in the dark.

Beetle flowers. These flowers tend to be either large and solitary, like Calycanthus or Magnolia, or small and aggregated into dense inflorescences (e.g., some Viburnum, Sorbus). Colors are often whitish or dull, and the flowers are open, with easy access to sexual organs and rewards. Odors are often strong and, to a human nose, generally unpleasant. Beetles are considered to be relatively inefficient pollinators due to their smooth, hard exteriors unsuited to adhesion of pollen, their chewing mouthparts, and their ungainly movements.

Bird flowers are usually red and very sturdy. Birds are relatively clumsy (except hummingbirds) and delicate flowers wouldn't stand up to the abuse. These flowers have evolved little or no odor since a bird's sense of smell is very poor. In our part of the world, you may know the red columbine or cardinal flower. Both are bird pollinated. If you have hiked in Rocky Mountain alpine meadows with a red backpack or red hat you have probably been bomb-dived by hummingbirds that check out any red-colored object as a potential food source.

Other pollinators are ants, bats (very common in the tropics) and a variety of small mammals.

WETLANDS.

These habitats range along a gradient from permanently flooded to periodically saturated soil and support hydrophytic (water-loving) vegetation at some time during the growing season. Our greenhouse has plants from ponds, marshes, and bogs. One of the most unusual types of hydrophytic plants are carnivorous plants.

Carnivorous plants are usually in bogs where the nutrient content of the substrate is low, and water and sunlight are abundant. Carnivorous plants can obtain nitrogen and phosphorus by digesting the proteins in the animals they capture.

Look for: CARNIVOROUS PLANTS

A surprisingly large number of plants are able to catch and digest insects by means of specialized leaves. They include the Venus fly trap (Dionaea muscipula), sundews (Drosera), pitcher plants (Sarracenia, Nepenthes), butterworts (Pinguicula), and bladderworts (Utricularia). This carnivorous habit has arisen in six families, fifteen genera, and approximately 500 species, and always in plants specializing on nutrient-deficient environments. Thus, the carnivorous habit is a means of securing those nutrients that are in limited supply and not a means of securing energy since all of these plants are photosynthetic.

Venus fly trap (Dionaea muscipula). Insects crawling on the leaf surface contact trigger hairs (easily seen with naked eye) which initiate the closing of the leaf. Enzymes are secreted by surface cells of the leaf, digesting the insects. Please do not attempt to trigger the leaves. They probably won't react (too old, or too tired due to visitor abuse). These plants are native to the Carolinas.

Sundews (Drosera spp.) These plants are common in the bogs of Pennsylvania. Notice that the leaf blades are covered with long sticky hairs. Insects get stuck and in their struggle, trigger the hairs which then bend toward the leaf surface where the insects are finally digested.

Pitcher plants (Sarracenia spp., Darlingtonia californica). The pitchers (modified leaves) have stiff rims with nectaries to attract insects. Many insects fall into the pitcher and cannot crawl out because of the stiff downward-pointing hair zone and the waxed, slick regions on the pitcher walls. Sarracenia bogs are common throughout the East while Darlingtonia bogs occur in Oregon and California.

Tropical pitcher plants (Nepenthes spp.). These are beautiful epiphytes in which the leaf midrib is prolonged into a tendril which bears a pitcher at its tip. These pitchers are not designed for water storage, If they were meant to trap rain water, why put a lid on them? In fact, they are for insect-trapping. It is very rare for epiphytes to also be carnivorous. Despite the presence of digestive enzymes in the pitchers, there are certain species of algae and even insect larvae which live a happy coexistence with the plant while immersed in the fluid. How they withstand the enzymes which digest other creatures is uncertain.

Butterworts (Pinguiculaspp.). The leaves of these species ensnare prey with a sticky glandular secretion. Once caught, an insect is enrolled by the leaf margins and digested or, in some species, is covered by digestive fluids that fill a dish-like depression that forms around the prey.

Bladderworts (Utricularia spp.). Highly sophisticated bladder traps of these species open with extreme rapidity to catch tiny prey. Borne underwater, in wet sand, mud, or moss, or in bromeliad tanks, prey are pushed into the bladders by water sucked into the vacuum created within the bladder.

TROPICAL AND TEMPERATE FORESTS.

The term "tropical forest" brings to mind images of lush green jungles of the Amazon. Tropical forests, however, embrace more than rain forest, they also include seasonally wet forests and dry forests. Likewise the term "temperate forest" conjures up thoughts of a Pennsylvania oak-hickory forest or a Michigan beech-maple mature forest. However, in spite of their name, temperate forests do not always exist in a temperate environment. They occupy topographic positions that range from low-lying lands to mountaintops, and environmental condi tions that range from warm and semiarid to cold and wet. Temperate forests include coniferous, deciduous, or mixed stands.

Look for: CYCADS AND FERNS

The cycads are palmlike plants (to your right and left on the tables just past the carnivorous plants) found mainly in the tropics and subtropics. These bizarre plants, though relatively uncommon today, were so numerous in Mesozoic times (220 million years ago) that this era is often called the "Age of Cycads and Dinosaurs". We have two representatives of this group in the Bucknell collection, Zamia and Cycas. In cycads, pollen and seed cones are borne on different plants.

The ferns are unique among seedless vascular plants in their possession of megaphylls, a large leaf with several to many veins. Ferns are abundant in the fossil record from the Carboniferous period (some 300 million years ago) to the present. In both form and habitat, ferns exhibit great diversity, ranging from the small aquatic Azolla to huge tree ferns to epiphytes (air plants). Many ferns have a fleshy underground rhizome with adventitious roots arising near the bases of the leaves. The leaf or frond is the conspicuous part of the sporophyte. Commonly the fronds are compound with the lamina divided into leaflets, or pinnae, that are attached to the rachis, an extension of the leaf stalk, or petiole. Typically the young leaves are coiled in the bud and appear like "fiddleheads". Most ferns are homosporous with the sporangium (spore producing structure) on the lower leaf surface, on specially modified leaves, or on separate stalks. The sporangia commonly occur in clusters called sori.

Look for: TROPICAL RAIN FOREST FORM

Forests that occur at relatively low elevation and have year-round rainfall are usually known as "tropical rain forests". The following features are characteristic of such forests.

Evergreen plants. "Evergreen" does not mean that such plants never lose their leaves. It means that individual leaves remain on the plant for one or more years. Thus, the plants always have younger leaves present when older ones are shed.

Trees predominate. The high rainfall encourages growth of trees. The canopy formed by the dense tree growth lets very little light through to the forest floor, so an understory of herbaceous plants and woody shrubs is discouraged. The floor of a rain forest is generally open as rain forests are not the "impenetrable jungle" that you may have heard about. Jungle occurs along streams and rivers or where disturbance has resulted in enhanced light levels at the forest floor.

Rich in vines. Over 90% of known species of climbing plants occur in tropical rain forests. Climbing plants have an advantage over trees in that they can grow rapidly into the high light environment of the forest canopy without expending a lot of energy on trunk growth.

Epiphytes are abundant. One solution to the problem of obtaining light in a dense rain forest is to grow attached to the trunks or branches of trees. About 25,000 epiphytic species are known (10% of all vascular plants) with the vast majority being epiphytic orchids.

Shade-tolerant epiphytes grow on the trunk or on the lower branches of trees and usually do not have special adaptations for preserving water since they are not exposed to direct sunlight. Shade-intolerant epiphytes, growing in the upper branches of the canopy where they are exposed to the desiccating effect of bright sun and wind, are invariably xeromorphic.

Simple leaves with entire margins are common. Simple refers to leaves that are not divided into leaflets (compound) and entire refers to a lack of lobes on leaf margins. Leaves on trees such as oaks or maples have well-developed lobes while Magnolia leaves are entire.

Drip tips, pointed extensions of the leaf, are common in tropical rain forests. Of 41 species studied in tropical rain forests of Sri Lanka, 37 had drip tips. Their function is uncertain, but is has been well argued that drip tips enhance water runoff and thus leaf drying - a feature that would decrease the epiphytic load of algae, fungi, lichens, and mosses on leaf surfaces.

Dieffenbachia and Monstera spp. (Araceae, same family as philodendrons and skunk cabbages). These plants are climbers in the rain forest, although here they are potted.

Monstera deliciosa owes its wonderful name to its delicious, edible fruits. These plants look much like the philodendrons, but notice the holes in the leaves. The holes allow light to reach the lower leaves that would otherwise be completely shaded.

Ficus elastica (fig), Psidium cattleianum (guava), and Aglaonema sp. are excellent examples of plants with drip tips.

Strelitzia reginae (bird-of-paradise) is bird pollinated; it provides a wobbly landing platform from which birds can feed. However, as the birds rock back and forth, they get pollen spread on their bodies. Try wiggling the platform. Can you envision how it works?

Look for: EPIPHYTES (air plants)

Epiphytic orchids. These plants are mostly in pots in our greenhouse growing in Osmunda fiber, but in the tropical forests where they are native they would be attached to tree trunks and branches. Examine our demonstration tree trunk (on the west windowsill) with epiphytic orchids and bromeliads growing in a more natural state. Look for those xeric features that are associated with orchid species which are shade-intolerant epiphytes.

-thick, leathery leaves
-pseudobulbs (swollen, water-storing stem regions)
-air roots covered with velamen (a special water-storing
tissue...appears white on dry roots)

Look at any orchid flowers that may be in bloom and note their complexity. The various colors, shapes, knobs, and bumps of each flower are the end product of coevolution with some particular species of insect, usually a bee. The specialization is often so narrow and the relationship so symbiotic that neither the plant nor the insect species can survive if the other goes extinct.

Epiphytic ferns. Look for the staghorn ferns hanging from the ceiling, Platycerium sp. These ferns have 2 kinds of leaves: the antler-shaped leaves do most of the photosynthesis while the rounded shield leaves are pressed flat against tree trunks to create a space in which debris collects. Staghorn fern roots penetrate this debris to pick up water and minerals. Often there is a symbiotic relationship between this fern and ants which colonize the debris. The ants feed on an amino acid-rich nectar produced by glands on the leaves and the plants gain minerals from debris more rapidly because of ant-enhanced breakdown of debris.

Epiphytic bromeliads. There are two types of epiphytic bromeliads (pineapple family) in this room.

Tank plants. We have numerous examples of this type growing along the glass wall separating the research house from the museum greenhouse. You can easily see how the tightly imbricated leaves (overlapping and pressed against each other) produce water-storage tanks. The tanks, evolved to catch and hold rain water, are miniature ecosystems with many other organisms living in them. Animals found in bromeliad tanks range from mosquito larvae to frogs.

"Air plants". You will see another type of epiphytic bromeliad on the misting water supply over the carnivorous plants. This one is the familiar "Spanish moss", Tillandsia usneoides. It is a common epiphyte in the southeastern U.S., growing not only in tree canopies but also on telephone wires. They have no mechanism at all for storing water like their relatives, the tank plants. The white fuzz you see covering the plants is an adaptation which these plants evolved to obtain water. This dense coating of complex hairs or scales is highly specialized to absorb dew or occasional rain water and transfer water to the internal photosynthetic tissues. Minerals are obtained in small quantities from dust or from rain water.

If you look carefully, you may see a tiny greenish-yellow flower here and there. Vegetative form is so variable that it is nearly useless in classifying plants. It is the flower which enables botanists to place this plant in the pineapple family.

Flowers are very conservative, changing little within a family, while there is rapid and extreme evolution in vegetative form. Can you think of an explanation for this fact?

Look for: CONIFERS

The conifers include the redwoods, pines, firs, spruces, and the like -- many examples of these can be seen on our campus. The history of the conifers extends back at least to late Carboniferous times (290 million years ago). Their leaves have many drought-resistant features, and perhaps the origin of conifers occurred during the dry Permian period, when increasing world-wide aridity may have provided a powerful evolutionary stimulus.

Two conifer families, both primarily from the southern hemisphere, are represented in our greenhouse collection, both growing in the rain-forest center section, the Podocarpaceae by Podocarpus macrophylla and the Araucariaceae by Araucaria bidwillii. Podocarpus ranges north of the equator in Central America, Africa, and from Malaya to Japan. Curiously, the Podocarp family was formerly widespread in Asia, Europe, and North America, as well as the southern hemisphere. Withdrawal to its present range occurred in later Tertiary times (7 million years ago). Araucaria has about 16 species ranging from New Guinea to Australia and also occurs in Chile, Argentina, and Brazil.

Look for: ECONOMIC PLANTS

The Bucknell Greenhouse contains a good number of economically important plants of the tropics. Coffee, the savory culmination of the aristocratic banquet, substance of the beggar's plea, and morning eye-opener, is produced in the New World tropics and is largely consumed in the Americas and Europe. There are many species but the prominent of these is Coffea arabica. The coffee plant is a shrub with glossy, deep-green, opposite leaves which like the fruit, contain caffeine. Fragrant white axillary flowers are borne two or three times a year in flowering seasons that correspond to times of dryness. The best and most productive coffee is grown in highland habitats, where constant, moderate temperature and frequent cloud mists stimulate growth.

Tea consists of the dried tip leaves of Camellia simensis native to southwestern China and northeastern India. The tea plant, left unpruned and unplucked, grows as high as 10 m. It bears thick, alternate, elliptic, serrate leaves, which possess numerous oil glands (the essential oils they contain produce the tea flavor) and the alkaloid caffeine. Some teas (Brazilian) contain high tannin content and give "body" to the beverage.

Among the wide diversity of tropical fruits, the banana (Musa species) stands out as one of the finest. The plantain (a starchy banana) bears a starchy, green-skinned fruit that is an important staple in the tropics. It is eaten baked, boiled, or fried. The banana plant is a tall, coarse herb rising as much as 10 m from a fleshy rhizome. The ensheathing bases of the petioles form the "stem" of the banana "tree". Each "stem" bears a terminal pendulous inflorescence in eight to 14 months, and after fruiting dies.

Citrus fruits, represented in our collection by Citrus limon (lemon) and C. mitis (calamondin), include oranges, lemons, limes, tangerines, grapefruits, kumquats, and more. The majority of citrus species are native to southeastern Asia but are now cultivated world-wide in subtropical climates. The commonly cultivated species are small trees with mycorrhizal roots and oil-gland-bearing leaves.

The pineapple is a native of the western hemisphere tropics. The pineapple genus, Ananas, is a member of the Bromeliaceae, a family predominantly composed of epiphytes. It is a coarse, rosette-form terrestrial biennial with long, stiff leaves that are usually spiny-margined. An erect central stalk bears an oblong head of flowers that upon maturation produces the characteristic multiple fruit.

The loquat (Eriobotrya japonica) bears plum-size fruits reminiscent in flavor of apples or pears (it is in the same family, the Rosaceae). It is widely grown in Japan, China, India, and the Mediterranean area, and to some extent in the New World subtropics.

Guava (Psidium species) has been distributed to practically all tropical lands from the Amazon basin. It often becomes naturalized and behaves as a weed. The guava is a small tree with coarse, opposite leaves. The white axillary flowers arise on new wood and develop the globose, gritty acidic, apple-like fruits used to make a dessert marmalade. Guavas can also be eaten fresh or in pie, or the juice extracted to make a drink.

Cardamom, an ingredient of curry powder and seasoning in many types of sausage, is the highly aromatic, dried fruit and seed of Ammonum cardamom. Cardamom plants are tall, coarse, large-leaved perennial herbs typical of the ginger family.

Vanilla is obtained from the fermented pod of climbing orchids (genus Vanilla) indigenous to tropical America.

Look for: ANT-PLANT ASSOCIATIONS

Dischidia sp. (milkweed family). These are fleshy epiphytic plants of SE Asia. Many species bear inflated, hollow leaves which are specialized as "ant leaves". During droughts which cause abscission of other leaves, the ant-leaves persist.

Myrmecodia sp. (coffee family). Notice the fattened, tuberous stem. Although it may not be apparent, this plant is also an epiphyte. The tubers contain a network of large cavities in which ants live. The usefulness of the ants to the plant is their provision of mineral elements to the plants. In return, the plants bear ant-attracting nectaries. What are some of the possible ways in which the presence of ants might be advantageous to plants?