720 SCHOOL SCIENCE AND MATHEMATICS

LIVING PLANTS FOR ECOLOGYAND PHYSIOLOGY

BY EDWIN D. HULLHull Botanical House, Gary, Indiana

GENERAL

The purpose of this paper is to discuss those living plantswhich are most useful in the study of ecology and physiology.No attempt is made at a complete survery, but only to showwhat is little or not at all known, or in the case of familiar plantsthose about which new data can be given.Few plants (these are indicated in the paper) will withstand

the severe conditions of the school room. The others must begrown under glass, for which a greenhouse is best, but if thisis not available then a contrivance known as the Wardian Caseis a fair substitute. This is simplya box, of a size to be determinedby the needs of the teacher, with sides and top of glass, andplaced preferably close to a south window to afford a maximumof light. This can be built by a local carpenter for a reasonableprice.

ROOTS

Adventitious Roots: An excellent plant to show this type ofroot is the Water Pennywort (Hydrocotyle umbellata), foundin nature mostly on the coastal plain from Massachusetts toFlorida and Texas, but also occurring inland in Michigan, Indi-ana, and Minnesota. It is to be looked for along the margins ofponds and in swamps, in habitats that are little or not at allshaded. Given a wet soil and abundant sunlight the plant growsvery well in cultivation, sending out creeping stems which ateach node send out a single leaf, and many roots. Other speciesof Hydrocotyle may be tried.

Roots as Aerating Organs: Comparable in function to the^knees^ of the Bald Cypress are spongy, thick and white struc-tures which arise from the stems of the aquatic Primrose Creep-ers (Jussiaea). These are true roots, growing upward and servingas aerating organs. Perhaps the best of these is Jussiaea repens,obtainable from dealers in aquatics, and readily cultivated inshallow water.Water Roots and Root Pockets: Best of plants to show this is

the Water Lettuce {Pistia Stratiotes), native in the southernUnited States, obtainable from many dealers in aquatics, and

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easily grown in a vessel with about a foot of water and a bottomof rich soil. The roots are produced in great abundance, andshow very conspicuously the curious root pocket of aquatics.

LEAVES

Photosynthesis in Green Tissue Only: The best for this purposeseems to be a well known foliage plant, the Silver Leaf Geranium,a variety of the common Fish Geranium {Pelargonium hor-torum). The leaf has a white margin, varying in width in differ-ent leaves, and destitute of chlorophyll. The plant will do bestin a rather cool atmosphere and considerable sunshine.

Release of Oxygen during Photosynthesis: The plant commonlyused for this experiment is the Water Weed {Elodea canadensis),common in slow streams and ponds, and in a giant form, usuallycalled Anacharis, sold by dealers. It is only necessary to pointout that much more satisfaction will be had if the wild form isused, as the giant Anacharis has, in some cases at least, givenno satisfaction at all.

Leaves as Reproductive Organs: The classic plant to show thisis the Life Plant {Bryophyllum pinnatum). To get the best re-sults it is necessary to place the leaf on moist soil and keep ina humid atmosphere. If kept dry only roots are likely to appear.Best of all, however, is the Water Fern (Ceratopteris thalic-troides), a floating plant with a native range like that of theWater Lettuce, and easily grown under the same conditions,and offered by dealers in aquatics. Even small fronds produceyoung plants in abundance over the upper surface. Anothervery good plant is the Hen-and-Chickens {Echeveria secunda),a common bedding plant, much like the well known HouseLeek, but differing in its bluish foliage. Leaves should be care-fully broken off, and then treated like Bryophyllum, when newplants should soon appear at the broken ends.

STEMS

Photosynthesis by Stems: (a) Ordinary Stems: This topic is besttreated in three divisions. In the first the leaves are scale-likeand do not function. A very good plant in this respect is thePrickly Pear Cactus {Opuntia\ easily grown from seed, whichshould germinate within a week if planted in a sandy, warmand moist soil, or it can be secured in a more advancedstage. This plant should live in the school room without spe-cial treatment. Opuntia has many species, most of which are

722SCHOOL SCIENCE AND MATHEMATICS

in the southwest, but one, 0. vulgaris, is common in the east,and another, 0. Rafinesquii, is common in sandy or gravellysoil in the central states. In the second category are leaves re-duced in size though still functional, but appearing late andfalling early, the stems being bright green and doing most of

Upper, left to right. Hypocotyl of Flax Seedling with adventitious buds;Diagram of Ruscus aculeatus (L-leaves, C-cladophyll, F-flower).Lower, left to right. Leaf of Water Fern (Ceratopteris) with young plants;Aerating Root of Jussiaea repens (OR-ordinary roots).

the work. Here belongs the Scotch Broom (Cytisus scoparius),a European plant naturalized in sandy barrens near the Atlanticcoast in Nova Scotia, and from Massachusetts southward. Seedsor plants can be obtained. In the third category the leaves arelarge, but yellowish green, and deficient in chlorophyll, in con-trast to the stems which are a brilliant green. Here are cacti

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belonging to the genus Pereskia, the only cactus group whoseleaves are not reduced to scales.

(&) Cladophylls: These are stems which superficially resembleleaves. The plant most easily obtainable is a species of orna-mental Asparagus (Asparagus Sprengeri\ which is possibly ableto endure school room conditions. A better form of Asparagus,having broader and more leaf-like cladophylls is the florists^Smilax (A. asparagoides). Best of all plants in this connectionare species of Butchers Broom (Ruscus), in which not only thecladophylls are strikingly leaf-like, but flowers appear in thecenter of them, arising in the axil of a scale-like leaf. The mostavailable species is Ruscus aculeatus, often planted in the south-ern states, the sprays of which, dyed red, are commonly seenin Christmas decorations.

Tubers: An admirable plant to show tubers, and one easilygrown in the school room, is the Tuberous Sword Fern (PIephro-lepis cordifolia; N. tuberosa), closely related to the common Bos-ton Fern. Tubers are produced in great abundance on under-ground stems, and will send up new plants readily if removedfrom the parent, and placed horizontally just underneath thesoil.

Adventitious Buds: To show these flax seedlings are the best,either the common flax which furnishes linen (Linum usitatissi-mum), seeds of which can be had from the drug store, or theFlowering Flax (L. grandiflorum), to be obtained from seeds-men. The latter, perhaps, is somewhat better. Seedlings shouldbe allowed to stand for a few days until perfectly erect andsomewhat rigid then the plant should be severed just below thecotyledons, leaving only the hypocotyl along which buds shoulddevelop in abundance. Many (20 or more) seeds should be plant-ed, as some of the seedlings will probably die after the cut hasbeen made.

A NEW DICTIONARY

What is a study room without a good dictionary? The point to an entirearticle is frequently missed because one word is not understood. Studentslose hours of time trying to solve a problem they do not understand be-cause one word has no meaning to them. The most important single refer-ence book in all branches of study is the dictionary. Every home shouldhave a good one. G. and C. Merriam Co. have just brought out a new Web-ster. See their announcement in this issue.