SCHOOL IN THE OPEN.

Star (Christchurch), Issue 17865, 5 June 1926, Page 24 (Supplement)

SCHOOL IN THE OPEN.

STUDIES IN THE GREAT OUT-OF-DOORS.

(Rv

J. J. S. Cornes, 8.A., B.Sc.

The “Star” has arranged with Mr J. J. S. Comes, 8.A., B.Sc., to write a series of illustrated articles which will give teachers and others a fuller appreciation of the Great Out-of-doors. They will deal with various aspects of plant and animal life, as well as with inanimate nature. Questions and material for identification will be welcomed.

to far greater size than the wee prothallus that gave it birth. Here, then, we have an “alternation of genera-tions”-T-fern (spore-bearing generation), —prothallus (egg-bearing generation) fern—prothallus—fern, and so on. The egg-bearing generation is much the smaller. We shall see that in the next group it is the other way about. Bryophyta. This fourth group includes the mosses and liverworts. The Greeks called the moss “bryon," so that this group has been labelled the Bryophyta. Where are the spores of a moss produced? At the top of the leafy moss plant is a thin stalk bearing a tiny capsule (G in diagram). This capsule is full of spores, and when its lid breaks off, leaving little perforations like those in a pepper-pot, these spores are scattered on the wind by the swaying of the stalk. Is this stalk and its capsule part of the leafy moss-plant? In a sense it is not, for though it grew out ol the leaf a- moss below, and remains attached

The Classification of Plants. (Continued) CXYIII. Of the five big groups of plants, we have already studied three —two of them, being seed-bearers, and the third including the spore-bearing ferns and club-mosses. We saAv that in the case of a fern, a spore, falling to the ground, does not grow immediately to another fern, but first to a t inv heart-shaped “prothal]us." This bears egg-cells and male sperms, and so corresponds roughly to the flower of a flowering plant. The fertilised egg gives rise to another spore-bearing fern-plant, which is dependent awhile upon the prothallus, but soon sends down its own roots, becomes independent, and so can grow

to. and dependent upon, the moss, it is a separate generation—it is the whole of a spore-bearing generation, while the leafy moss is an egg-bearing generation, corresponding to the tiny prothallus of a fern. «. A fertilised egg at the top of the moss plant began growing to a sporebearing generation: But this, unlike the spore-bearing fern, never sends down its owjt root, but remains dependent upon the egg-bearer, and so cannot groAv to more than just a stalk and a bag of spores. Y hen we think of a fern plant, then? the leafy plant we have in mind is the spore-bearing generation—but when we speak of a moss, the leaf y plant we are thinking of is the egg-bearing generation, corresponding to a fern prothallus. and the . moss plant, like a prothallus, though it has stem and leaves of a sort, has no roots, but onlv root-hairs. And like a prothallus it |hc sexual bodies, producing sperms -.which swim to the egg-cells to j fertilise them. This egg, too, grows' into a little plant producing spores, only in this case the spore-bearer, as j we have said before, remains depend- } ent. small, and simple, just a capsule I on a stalk. Thallophyta. r l he plants below the Bryophvta usually have little differentiation into stems and leaves. This kind of plantI body is known as a thallus, so this fifth group is called the Thallophvta. It may consist of a single cell, or a string of cells, or a more complex body, as in seaweeds and toadstools. In some of the seaweeds there is an apparent differentiation into leaf, stem 1 and root, but these are just modified [ I portions of the thallus. Thus in a big brown seaweed, the “leaf” is just a flattened portion, the “stem” a thickened portion, while the “root” is merely an expanded hold-fast -or anchor, since the seaweed absorbs its food its whole surface from the seawater bathing it. These Thallophvires are often put under three y \ .Algae, Fungi, and Lichens. Algae. The Algae are plants which contain leaf-green (chlorophyll) and are therefore able to manufacture their own carbonaceous food. As examples, we have Protococcus, which gives the green stains on trees and walls, Spirogyn. and others forming the green slime m pools, and seaweeds of various tints of green, brown and red. Fungi. The fungi have no chlorophyll, and are therefore dependent on other organisms for their supply of carbonaceous food, either feeding on the living juices, when they arc called parasites (e.g. bacteria, potato disease) or on the substances formed by the decaying organisms. when they are termed saprophytes, (e.g. moulds, and' mushrooms). Lichens. Lichens are often mistaken for mosses, \-et how different, how much more lowly organised they are! They are really a kind of mixture of the simple algae and fungi, being* built up of fun-

gal filaments with A\-hich green algal cells are intimately associated, so that a compound organism of a self-support-ing nature is formed, a partnership where the fungal mesh work provides a home for the alga, which in turn makes carbonaceous food s for the fungus. Some lichens hang in mossy festoons like old men'.; beards, from trees, but the commonest merely form a crustlike covering on rocks. A'ct they arc common e\er\ Avhcre, and their different forms and tints give variety and

colour to the boulder, wall, or tree is clothed by them. (To be continued next Saturday)