Part 103. The Reproductive System - The Crowfoot Family

Part 103. The reproductive system. Turning now to the flowers of the marsh-marigold it will be noticed that they grow either at the tip of the main axis or on stalks which arise from the axils of upper leaves. On the side of the flower-stalks, or subtending them, may be sessile leaves or more or less scale-like leaf-members. Such leaves subtending a flower or a flower-cluster are called bracts,¹ or when borne upon a flower-stalk they are termed bractlets. The stalk of a flower or flower-cluster is distinguished as its peduncle.² We speak of a blossom or flower-cluster as an inflorescence.³ Thus we say that the inflorescence of the marsh-marigold consists of a terminal flower, and a few axillary ones, with bracts and sometimes bractlets. It should be noted that the terminal flower opens before the lateral ones, thus putting an end to further elongation of the main axis. Such an inflorescence is therefore called determinate. It is also described as cymose because the form of cluster which typically results from the determinate mode of growth is called a cyme.⁴ The inflorescence of the marsh-marigold is a simple cyme. A well-developed cyme is found in certain species of clematis. Here, as shown in Fig. 290, the axes repeatedly branch, making the cyme compound. In compound inflorescences the ultimate flower-stalks are called pedicels.⁵ A whorl or cluster of bracts is an involucre;⁶ while the term involucel⁷ is applied to a whorl of bractlets. Thus the wood-anemony has an involucre of three leaf-like bracts situated far below the solitary flower. These are called bracts because in related species bracts similarly placed subtend peduncles, although as must be obvious the distinction between bracts and bract-lets in such cases is rather arbitrary. Fennel-flower has an involucel of a few large bractlets very near the blossom. Most of the crowfoot family have simple, cymose inflorescences, usually of only a few flowers as in crowfoots, columbines, and the Christmas rose. Often, even in the genera mentioned, the flowers may be solitary, and this is usually if not always the case in mouse-tails, anemonies, fennel-flowers, and peonies.

In contrast with these determinate inflorescences in which the terminal, upper, or inner flowers are the older, are inflorescences of the indeterminate type shown in baneberries and monkshoods. Here the upper flowers are the younger, and the main axis or rachis ⁸ may elongate indefinitely, developing new flowers as it grows. When, as in the examples given, the main axis is longer than the peduncles, the cluster is termed a raceme.⁹ So typical is this of the indeterminate form of inflorescence that the term botryose ¹⁰ of similar implication is given to it as being in significant contrast with cymose.

¹ Bract - L. bractea, a thin plate.

² Pe-dun'-cle - L. pedunculus, diminutive of pes, pedis, foot.

³ ln-flor-es'-cence - L. in, in; florescere, begin to blossom.

⁴ Cyme - Gr. kyma, a young sprout, because the younger flowers arise like sprouts from below. (Pronounced siem.)

⁵ Ped'-i-cel - L. pedicellus, diminutive of pediculus, dim. of pes, pedis, foot.

⁶ In'-vo-lu-cre - L. involucrum, - involvere, enwrap.

⁷ In-vol'-u-cel - L. involucellum, a little wrapper.

⁸ Ra'-chis - Gr. rhachis, backbone.

⁹ Ra-ceme' - L. racemus, a bunch of grapes.

¹⁰ Bot'-ry-ose - Gr. botrys, a bunch of grapes.

From the above it appears that in describing and naming inflorescences botanists have regard either to the manner in which the branches arise and the relative position of the oldest flowers, or else to the general form as modified by more obvious features, like the relative lengths of the internodes. It is desirable to keep these two points of view distinct.

Viewed as to their system of branching, simple inflorescences, such as most of those we have been studying, are either of the cymose or the botryose type. Under the head of cymose inflorescences we should include a solitary flower which terminates a leafy axis, as in the wood-anemony; while a solitary flower, which, like that of the mouse-tail, springs from the axil of a foliage leaf would more logically be called botryose. When the branches of an inflorescence branch again it becomes compound, as in our example of clematis, (Fig. 290) which has a compound cyme, or cyme of cymes.

As to general form we may here distinguish: (1) racemose inflorescences or racemes, like those of monkshood and baneberry, which are simple and have pedicels all shorter than the rachis, thus giving an elongated cluster; (2) paniculate ¹¹ inflorescences or panicles, which are more or less elongated and compound, as in Fig. 293; and (3) corymbose ¹² inflorescences or corymbs (Fig. 290) which have the outer pedicels or branches about as long as the rachis, and those nearer the center progressively shorter so that the cluster as a whole is broad and more or less flat-topped. Corymbs often become racemose as they grow older, and compound corymbs, paniculate. Some botanists would restrict the terms raceme, panicle, and corymb to indeterminate inflorescences; but in practice these names are applied indiscriminately also to inflorescences of the determinate type which have assumed the forms above defined. Thus we may speak of a racemose, paniculate, or corymbose cyme.

¹¹ Pan-ic'-u-late - L. panicula, a tuft.

¹² Cor-ymb'-ose - L. corymbus, a cluster of flowers.

In a flower of marsh-marigold we recognize many organs similar to those already observed in the flax but with some important differences. Thus in the center of the flower we find a cluster of pistils each with a single stigma, style, and ovulary cavity instead of a single pistil with several styles and stigmas and a single ovary with several cavities. Such simple pistils as those of the marsh-marigold are called carpels¹³ and are regarded as representing each a single egg-sac leaf just as a stamen is a single pollen-sac leaf. Taken together the carpels form the gyncecium ¹⁴ of the flower, while the stamens collectively form the androecium.¹⁵ Near the base of each carpel is a gland that secretes drops of a sweet fluid, called nectar ¹⁶ Which attracts insects, and from which they make honey. In each ovary of the marsh-marigold, as will be noticed, there are several ovules attached to that part of the wall lying nearest the center of the flower along a line running from top to bottom-such a line as would be made by the edges of a folded leaf where they came together. Thus the carpel of a marsh-marigold may be likened to a leaf bearing ovules along its edges and these joined so as to form an ovary. That part of an ovary wall which bears the ovules is called the placenta; ¹⁷ and when as in this case it extends along the front side of the ovary (that toward the center of the flower) the placenta is said to be ventral.¹⁸ The opposite side or back of the carpellary leaf, commonly marked by a ridge representing the midrib, is distinguished as the dorsal¹⁹ aspect.

¹³ Car'-pel - Gr. karpos, fruit, as being essentially the fruit producing part.

¹⁴ Gy-noe'-ci-um - Gr. gyne, female; oikos, house.

¹⁵ An-drce'-ci-um - Gr. andros, male.

¹⁶ Nec'-tar - Gr. nektar, the drink of the gods.

¹⁷ Pla-cen'-ta - L. a little cake, from its cake-like form in certain cases.

¹⁸ Ven'tral - L. venter, belly.

¹⁹ Dor'sal - L. dorsum, back.