Part 98. Morphological units. We have seen that the embryo flax is a miniature plant already possessing a stem-part, rudimentary leaves, and the beginning of a root. These parts we recognize as representing the main divisions of the plant, at least before it flowers, for we know that for many weeks as the plantlet grows it simply produces more root, more stem, and more leaves. If we examine minutely one of the leaf-buds (Fig. 280) we find it to contain a series of young leaves which are smaller and smaller as we approach the tip of the stem until finally they appear as mere lobes. Thus we see that a leafy shoot begins as a tiny dome-shaped mass of growing material, which as it elongates, becomes differentiated into (1) lateral lobes, which grow into leaves, and (2) a central or axial part constituting the stem which bears them. Soon in the axils of the young leaves appear growing points like the cone at the tip, and each of these becomes a bud which may develop into a leafy branch. Since corresponding parts arise at regular intervals, the whole shoot, especially as it grows older, takes the form of a series of segments or equivalent divisions each consisting of a leaf-part borne by a stem-section from which a bud or rudimentary branch may also develop. The embryo, we remember, had just these parts, and in addition bore a root. Often, such a shoot-segment cut from a plant and placed under favorable conditions for growth will send out a root, and develop other segments much as an embryo does; and, commonly, a cutting which consists of a single leaf attached to a bit of stem, is the least part of a flowering plant that can be made to grow independently. Hence such a segment consisting of an internode and its node, together with the leaf or leaves it bears, has been regarded as constituting, in a way, a unit of plant structure.