(figure available in print form)
A phreatophyte is defined by Webster’s Dictionary as “a deep-rooted plant that obtains its water from the water table or the layer of soil just above it.”
5
An example of a phreatophyte freshwater marsh tree is the Atlantic white cedar; a phreatophytic woody shrub is the alder; and a phreatophytic herbaceous plant is the cattail.
A hydrophyte is defined by Webster’s Dictionary as “a vascular plant growing wholly or partially in water, requiring an abundance of water, growing in places too waterlogged for most other plants.”
6
Hydrophilic species include burden grasses, emergents, floating-leaf plants and submerged plants. All of these plants are herbaceous, meaning they are a nonwoody plant. Examples of hydrophilic freshwater marsh species are rushes, pickerel weed, and waterlilies.
7
Figure 3 depicts a cross-section of a bog. The same three categories of plants, based on their degree of tolerance of wet conditions, are also found in the freshwater bog. An example of a tolerant tree is the hemlock; a tolerant woody shrub is the highbush blueberry; and a tolerant herbaceous plant is the purple loosestrife. Phreatophytic trees are the tamarack and black spruce; phreatophytic woody shrubs are buttonbush and sweet pepperbush; and phreatophytic herbaceous plants are pitcher plants and sundews. Hydrophilic freshwater bog plants are spatterdock and bladderwort.
If the area in question exhibits some of the characteristics shown in Figures 2 or 3, the flora should be examined to determine whether there is a predominance of wetland species.
The Curriculum Unit,
Inland Wetland Area Exploration
, provides guidelines and a survey form for teachers to use when taking their students on a field trip. Parameters included on the survey form are flora, fauna, water chemistry, physical characteristics of the wetland area, and land use. Background on water chemistry, physical characteristics of the wetland area and land use can be found in the unit,
Know Your Watershed,
1984, Teacher’s Institute. A good reference book to identify fauna is
A Guide to the Study of Fresh Water Biology
and the Peterson Field Guide Series in the Teacher and Student Bibliography
.
After it has been determined that a wetland is involved, the individual can then notify the regulatory agency. The section of this paper,
Importance of Inland Wetlands and Connecticut Wetland Laws
describes how and who to contact should you suspect an inland wetland is being threatened.
8
A PLANT OF THE HYDROPHILIC ZONE IN THE BOG OR MARSH, Nymphaea odorata OF THE Nymphaeaceae FAMILY, THE FRAGRANT WATERLILY
An inland wetland plant of particular beauty is the waterlily. Its distribution is worldwide and it occurs in colors ranging from white to blue, yellow and red. We enjoy waterlilies for their beauty and they also have become one of the plant indicators for inland wetlands. Biologists are particularly interested in the waterlilies because they form large crystals in their leaves. The following is a discussion of the waterlily, its adaptations to its aquatic environment and of the crystal structures that form in its leaves.
Man has used the seeds and tuberous roots of waterlilies as food for centuries. We find mention of them as far back as Egyptian times where, besides being an important food, they were used in social and religious instances. The waterlily, or lotus, was placed upon the bodies of the dead. It was also the emblem of the Nile god, being an evident product of the river. An historian tells us, “When the Egyptians approached the place of divine worship, they held the flower of the lotus in their hand, indicating that that man had proceeded from a well-watered or marshy land, and that he required a moist rather than a dry ailment.”
9
Waterlilies are found in the shallows of slow streams and still waters all around the world. They, like their fellow freshwater seed plants, are derived from terrestrial ancestors. They have become modified in various ways to their new habitat—development of buoyant stems or floaters, adaptations in the shape of the leaves, and in some, underwater pollination.
10
Although some have rhizomes, a mass of roots, the greater number have a tuberous stem from which many fibrous roots pass downward and anchor the plant in place. The stems of the waterlily branch infrequently; however, they have bunches of tubers growing from the sides. The tubers can float and are easily detached from the plant. Thus the tubers serve to distribute the plant widely. Figure 4 shows the tuber of a waterlily.
Few genera of flowering plants show such variety in size and color as the waterlilies. Shades of white, yellow, red and even royal blue do occur. The opening of the flower occurs at a particular time of day for each species. The process of opening and closing takes nearly an hour. Most open during the day, but some open at night. The flowers are pollinated by insects and on the last day of opening, the fertile flower sinks into the water and disintegrates. The fruit, technically a berry, forms underwater near the bottom.
The waterlily leaf, or lily-pad, is familiar to many of us. The leaves of waterlilies can be submerged. floating or aerial. Aerial leaves are rare, but do occur in conditions of overcrowding.
The submerged leaves are narrower in shape, more like a deltoid, than are the floating leaves. It is surmised from the richness of their chlorophyll that they play a major role in photosynthesis. Figure 5 illustrates a typical waterlily and the slide show that accompanies the unit also shows the waterlily’s anatomy, especially of the leaves, along with pictures of the plant community of Cedar Swamp.
The stalks of the leaves, or petioles, may range in length from a few centimeters to six meters, depending on the depth of the water. They grow to a length that allows the leaf some freedom in floating. The floating leaves are especially adapted so that the stomata, openings through which gases pass, occur only on the top of the leaf. In nonhydrophytes, the stomatas occur on both sides. This is of course a necessary modification, since only the top of the leaf has contact with the atmosphere.
The floating leaves are very round in shape, thus maximizing their potential for surface area and thus their photosynthetic potential. The leaves also provide the outlet for transpiration (the loss of water vapor).
11
Cellular Biology and Calcium Oxalate Crystal Formation
In special cells of the waterlily, a phenomenon occurs that has fascinated scientists for ages, the formation of crystals. The deposition of inorganic material in living plants and animals is a common occurrence.
It culminates in the beautiful home of the corals, spiral shells of snails, and the complex bones of vertebrates, including humankind. And we find deposits of calcium oxalate (CaC2O4) in the stems, roots and leaves of many plants. The mode of deposition of these crystals in the waterlily is not known. However, much speculation exists as to why these crystals are formed, and how. The following will be a discussion of this speculation.
There are two components that are of importance to our discussion; one is oxalic acid, and the other calcium.
Oxalic acid is an interesting organic compound, since except for carbon dioxide, it has the highest proportion of oxygen to carbon and thus is a frequent end-product of oxidation (an important reaction of energy transfer in all living things). So it is not surprising that we find oxalic acid extensively in nature, sometimes as the free acid, but more commonly as the potassium or calcium salt. It is believed by many that oxalic acid is a useless end-product of metabolism. This view is supported by the fact that many plants cannot utilize the acid, or its salt. Those who believe this theory regard oxalic acid to be toxic, and feel that it is rendered harmless by precipitating it as the calcium salt. However, some believe that oxalic acid is produced to rid the plant of excess calcium ions. The fact that some plants, such as begonias, can store large amounts of oxalic acid without any harmful effects, and that several reports show that oxalate formation is related to the supply of calcium, support this view.
12
Calcium is essential to the growth of all plants and most plants must take in substantial amounts for normal growth. Figure 6 shows the calcium cycle in plants. Calcium is taken up in the soil by the roots. The movements of calcium through the plant is believed to be through the transpiration stream. Calcium is lost from pithy tissues through decay, abscission (the dropping off of plant parts), gustation (the exudation of liquid from leaves) and leaching (the downward movement and drainage of minerals through the soil by percolating water).
13
The principal forms of calcium oxalate occurring in nature are the monohydrate whewellite (CaC2O4.H2O) and the dihydrate, weddelite [CaC2O4.(2 + x) H2O, where 0.5]. Whewellite is more stable, and is the most common form
14
Calcium oxalate crystals are bound generally intracellularly, often in cells called idioblasts, a`specialized cell entirely different from its neighbors. The crystals may occur as single and massive (styloids); as large single prisms or pyramids (prismatic); as needles shaped in packets of as many as 2,000 crystals per cell (raphides), multiple star-shaped (druse), or in fine crystals (crystal sand).
The crystals are produced and contained within a vacuole, a membrane bound structure that is found within the cell’s cytoplasm, a watery fluid in which the organelles of the cell float. Crystals are formed in crystal chambers formed by membranes. The crystal vacuole is surrounded by a membrane called the tonoplast.
The mechanism that brings the calcium and oxylate together is unknown. It has been suggested that a calcium pump may be present and that it transports calcium from the cytoplasm to the chamber which is already loaded with oxalate.
15
The genus Nymphaea is somewhat different from other plants observed. The crystals are associated with the cell wall; the mode of the crystal formation is still unknown. Figure 7 shows a cell with crystals. This is a scleroid cell (a cell which is part of the plant’s structural support system, which is variable in form and often branched). It is somewhat difficult to illustrate, but under polarized light, the crystals in these cells reflect the light, seen in Figure 7 as the light areas.
Figure 8 illustrates an electron micrograph showing a transverse section through an arm of the crystaliferous scleroid of the waterlily. This cell has a secondary cell wall, the innermost layer of the cell wall (labeled SW) formed in certain cells after cell elongation has ceased. Three calcium oxalate crystals are embedded in the secondary cell wall. A primary cell wall (PW), the wall deposited during the period of cell growth, separates the exterior of the cell from an intracellular airspace (IS) and a small area of cytoplasm (CY) can be seen towards the bottom of the picture.
16
The Role of Calcium Oxalate Crystals In Plants
Other species of plants have calcium oxalate crystals; the reason for crystal formation varies with the species and with the environmental conditions.
17
In some plants, such as the Jack-in-the-Pulpit, the crystals may be formed to discourage predation from insects, snails, and other animals. One bite of the stalk will prove it to you by the burning sensation caused by its raphides.
18
The lupin plant shows us another possible reason for the role of calcium oxalate production in plants. In most species, once the crystals are formed they remain unchanged. In this plant, however, when the seeds germinated, the crystals dissolved, then disappeared.
19
Hence, the crystals may provide a valuable source of calcium and oxalic acid.
And, supported by many, is the theory that calcium oxalate is a useless and possibly adventitious product of metabolism.
20
Not much has been written on its possible structural or skeletal significance. It is interesting to note that in the case of Nymphaea, the crystals are associated with the cell wall of a structural cell of the leaves. The particular conditions of life have impressed themselves strongly upon the forms and functions of the waterlilies, as previously discussed. Once spread out upon the water surface, the leaves are subjected to the stress of currents in air and water. Perhaps the presence of these crystals may have something to do with the plant’s particular adaptations—an interesting question for further investigation.
