Part 99. Members of the plant body. A plant like flax is sometimes thought of as a colony of segments or in other words as a community of closely connected individuals each consisting of a stem-part and leaf-part, and capable of producing a root, and so leading an independent existence. On this view each segment would correspond to an individual animal and its leaf-part and stem-part would be likened to the members of the animal body, such as the trunk and the limbs. Without accepting this extreme view of what constitutes an individual plant-a view not in accord with what we have learned about the development of the shoot-it may still be convenient to regard the bodies of the higher plants as built up of segments, much as zoologists regard the bodies of many segmented animals like earth-worms and lobsters as consisting of a series of roughly comparable units; and, similarly, just as the limb of an animal viewed as one of the main divisions of the body or of a segment is called a member, so the main divisions of a plant-segment-the stem, the leaf, and the root-viewed not as organs but merely as parts differing in origin and position, may be conveniently distinguished as members of the plant body.

But the question at once arises, supposing it to be admitted that the vegetating plant may be roughly likened to a many-storied building, each story being a segment, and the whole supported on a root foundation, can we yet find corresponding units of structure in the flower? If the flower is composed of segments it is evident that the different members must be more or less disguised. As regards the floral envelopes we have already seen that their leaf-like nature is so thinly disguised that they are commonly recognized as "leaves of the flower." Indeed, we have only to suppose the internodes of the stem-parts to have remained as short as they were in the bud, while the leaf-parts expanded, to see that so far as origin and relative position are concerned, the floral envelopes are essentially like a leaf-rosette. But the stamens and the pistil present greater difficulties. Still, when we come to compare other flowers with those of the flax, we shall find much evidence going to show that even stamens and pistils correspond in large part to leaves. One sort of evidence-not indeed conclusive, but yet significant- is the occurrence now and then of monstrous flowers in which actual green leaves occupy the place of the stamens and pistil, much as if the organs had determined to throw off all disguise and exhibit their true nature.1 The proof of a theory is in the using; for the present it will be enough for us to have gotten a preliminary idea of what the segment theory means when applied to our typical plant.

1 The theory of floral structure which likens a flower to a leaf-rosette originated with the poet Goethe to whom it was suggested by seeing a green rose such as occasionally appears in gardens. This theory has proved to be a helpful means of understanding the relation of the various parts of plants to the fundamental plan of structure; but as it tells only part of the truth it has been somewhat misleading, and it requires to be modified considerably from its original form to be in accord with more recent views of vegetable morphology. As developed above, however, it is believed that the theory will be found to avoid the unwarranted assumptions which have brought into it discredit, and to retain the features which have made it useful, while at the same time such modifications are made as will render it a valuable means of conveying modern views.

Other questions, closely connected with the foregoing one, are, What members may a segment have? and, How may these be distinguished under all their disguises? The flax embryo, as we have seen, represents a segment reduced to about its simplest terms. We here recognize an axial member bearing lateral members,-the stem-part and the leaf-part,- one implying the other. When the root-part appears we have another member which is also axial, but differs from the stem in being without leaves. As the root elongates there appear near its tip numerous hair-like projections which differ essentially from leaves in being merely superficial outgrowths not continuous with the innermost parts as is the case with leaves. Superficial appendages of this sort often occur in other plants on the stem and leaves as well as on the root. Such more or less hair-like outgrowths are best regarded as parts of members rather than as members. In the essential organs of the flower we meet with a difficulty regarding the real nature of the pollen-sacs and ovules or egg-sacs as we may call them. In the flax they both might be taken to be parts of the peculiar leaves which we regard as forming the stamens and pistil. But there are other plants, as we shall see, in which an ovule appears on the very tip of the stem or axis, while in some cases pollen-sacs seem to grow directly from the stem. We can then hardly call such organs parts of a leaf. On this account and for other reasons which will appear later, we are led to regard both pollen-sacs and egg-sacs as distinct members of the plant body. We thus come to the conclusion that our typical plant viewed morphologically is made up of members of the nature of stem, leaf, root, pollen-sac, and egg-sac; and that the whole body may be furthermore regarded as -consisting of a chain of segments, each segment having at least a stem-part and a leaf-part and sometimes also other members.

A root-member may be defined in a general way as typically a descending axis; a stem-member as an ascending leafy axis; and a leaf-member as a lateral, transversely flattened outgrowth from a stem. Since stems and leaves imply one another, it is convenient to speak of them together as forming a shoot. Thus in our flax embryo the caulicle, cotyledons, and plumule constitute the shoot as distinguished from the root-part. A sac-member, such as a pollen-sac or an egg-sac, is really, as we shall see later, a spore-case essentially like that of Lycopodium (Fig. 166, 2). Pollen grains are spores; and each egg-sac contains one or more comparatively large spores within which an embryo arises. Thus a sac-member is known by what it produces. As to how these different members may be further distinguished we shall learn more fully when we come to compare other plants with our type.