PLANTS, Recapitulation in. The term, recapitulation, in plants and also in animals, is used to designate features of the embryogeny and early development of the individual. uOntogeny recapitulates is the usual classroom term, meaning that the individual, in its own development, repeats the history of the race. The frog is first a pollywog and then tadpole, before it finally reaches the adult stage. This is interpreted to mean — according to the recapitulation theory — that the frog's very re mote ancestors were adult at the pollywog stage; and that its less remote ancestors were adult at the tadpole stage. The frog, in its individual life history, repeats these phases of its ancestry. Zoological literature is full of il lustrations. In plants, illustrations of recapitu lation are just as numerous, but are not so widely known. In many trees and shrubs, the early leaves• of the seedling are quite different from the leaves of the adult plant. The Ginkgo, or Maiden Hair Tree, offers a good example. The leaves of the adult tree have an even, wedge-shaped outline (Fig. 1, D) or have a notch at the apex (Fig. 1, C), the latter condition suggesting the specific name, biloba, the scientific name being Ginkgo biloba. The leaves of the seedling, and also the leaves at the tops of young trees, do not have such a simple outline, but are deeply cleft (Fig. 1, B). This is significant, for the geological ancestors of Ginkgo —like the Baiera— have just such cleft leaves at the adult stage (Fig. 1, A). In the common larch (Larix) the seedling has simple, needle leaves, and such leaves are found on the first year's growth from any bud on the tree; but later, the leaves appear in dense clus ters on short spurs. In the pine, the seedling has short needle leaves, but later the leaves are longer and occur in twos, threes or fives on short spurs. Examples might be multiplied.
The early form of leaf is called a "juvenile" leaf, and many believe the seedling is passing through a stage which characterized its adult ancestors. All Pteridophytes (ferns and fern allies), which have two kinds of spores, furnish excellent illustrations of recapitulation. Sela ginella, a very common greenhouse plant, may be taken as an example. In its early develop ment, the megasporangium is just like the sporangium of a common fern which is to pro duce only one kind of spore. In Selaginella itself, the microsporangium looks very like the sporangium of a common fern. All of its spores reach maturity. In the megasporangium, the spore tissue develops just as in a fern and mother cells round off, as if to produce the usual four spores; but only one mother cell undergoes the expected division, giving rise to four spores, while all the rest of the mother cells disorganize and their substance is ab sorbed by the four spores. Selaginella repeats an ancestry in which the spores were all alike and all functioned. The protonema of a moss tails of recapitulation. In the oogonium of Focus eight nuclei are formed and each nucleus becomes the centre of an egg. In most of the other genera of the family, the eight nuclei are formed, but some of them disorganize, so that the mature oogonium contains only four or two eggs, or even only one. Fucus shows the ancestral condition. The others pass through the Fucus stage on account of this phase of heredity known as recapitulation. In studying the relationships of great groups, orders, fami lies, genera and even species, recapitulation fur nishes valuable suggestions. Consult Wilson, E. B., (The Cell in Development and Inherit ance> ; Spencer, Herbert, The First Principles of