Page:Encyclopædia Britannica, Ninth Edition, v. 4.djvu/151

Rh PISTIL.] BOTANY 141 plant, in which small cells, microspores (fig. 249), are found, each consisting of an (alter covering or exospore, and an inner or endospore. Within those microspores (the manner varying in different genera) smaller cells are formed, which are the mother-culls of the antherozoids. In this Vertical section of the disk-like receptacle of Liverwort (Mai-chant ia), showing nntheridia a, a in its substance. These antheridia are flask-shaped sacs con taining phytozoary cells. They communicate with the upper surface, and their contents are discharged through it. lietween the antheridia there are air cavities c, c, connected with stomata ., s. development of Lycopodiaceje we have parts which are analogous to those of the stamens in Phanerogams. The microsporangium evidently corresponds to the pollen-sac, and the microspores are the equivalents of the pollen- grains, the forms seen in such Gymnosperms as Cycad- acea; beincr the link connectinc; them with the hi&amp;lt;rhest forms. 249. Fie. 250. FIG. 245. Spore .?, of a Fern (Pleris lonyifolia) sprouting, giving off a root-like process, r, and a flat cellular expansion, p, called the prothallus or protliallium. On this expansion inithcridia and pistillidia are said to occur. FIG. 246. Fructification of Club-Moss (LycopoJium), situated in the axil of a leaf, I. It consists of a case containing minute cellular bodies, which are dis charged in the form of powder. Fir,. 247. Fructification of a Club-Moss (LycopoJium daratum). The branch is covered with minute pointed leaves, /; from it proceeds a stalk bearing at its extremity two spikes,/, consisting of modified leaves, with fructification. FIG. 248. One of the cases separated from the axil of the Club-XIoss leaf, opening by two valves, and discharging the minute Lycopod powder (microspores). FIG. 249. The small spore of a Rhizocarp (Pilularia globuliftra, Piliwort). The inner coat is protruded, and the outer coat has burst so as to discharge cellules containing spcnnato/oids. Some of the spcrmatozoids are separate, and are seen coiled up in a spiral form. FIG. 250. Antheridia from the prothallus of the Common Brake (Pteris aqttilina). a, an unopened anthcridium ; b, antheridium bursting at the apex, and dis charging free cellules, each containing a spermatozoid ; c, antheridium after the discharge of the cellules. 3. Female Organs in Phanerogams. The pistil or cjyiicecinm occupies the centre or axis of the flower, and is surrounded by the stamens and floral enve lopes when these are present. It constitutes the innermost whorl, and is the female organ of the plant, which after The pistil, flowering is changed into the fruit, and contains the seeds. It consists essentially of two parts, a basal portion forming a chamber, the ovary or germen, containing ovules or young seeds attached to a part called the placenta, and an upper portion, the stigma, a cellular secreting body, which is either seated on the ovary, and is then called sessile, as in the Tulip and Poppy, or is elevated on a stalk called the Plate I. xtyle, interposed between the ovary and stigma. The atyle 251. Fig. 252. Fig. 253. FIG. 251. Folded carpellary leaf of the double-flowering Cherry. In place of fruit the plant produces leaves. FIG. 252. Vertical section of the flower of Meadow-sweet (Xpircra). The pistil is apocarpous, consisting of several distinct carpels c, each with ovary, style, and stigma. The stamens are indefinite, and are inserted into the calyx. FIG. 253. Pistil of Broom, consisting of ovary o, style s, and stigma t. It is formed by a single carpel. The terms pistil and carpel are here synonymous. ifi not necessary for the perfection of the pistil. Like the Plate V. other organs, the pistil consists of one or more modified leaves, which in this instance are called carpels. When a pistil consists of a single carpel it is simple or mono- carpcllary (fig. 253). a state usually depending on the non- development of other carpels. When it is composed of several carpels, more or less united, it is compoimd or polycarpellary. In the first-mentioned case the terms carpel and pistil are synonymous. Each carpel has its own ovary, style (when present), and stigma, and is formed by a folded leaf, the upper surface of which is turned inwards towards the axis, and the lower outwards, while from its margins are developed one or more buds called omdes. That this is the true nature of the pistil may be seen by examining the flower of the double- flowering Cherry. In it no fruit is produced, and the pistil consists of sessile leaves (fig. 251), the limb of each being green and folded, with a narrow prolongation upwards, as if from the midrib, and ending in a thickened portion. The ovary then represents the limb or lamina of the leaf, and is composed of cellular tissue with fibro- vascular bundles, and an epidermal covering. The cellular tissue, or parenchyma, often becomes much developed, as will be seen particularly when fleshy fruits are considered. The outer epidermis corresponds to the lower side of the leaf, exhibiting stomata, and sometimes hairs ; the inner surface represents the upper side of the leaf, being usually very delicate and pale, and forming a layer called sometimes epithelium, which does not exhibit stomata. The vascular bundles correspond with the veins of the leaf, and consist of spiral, annular, and other vessels. In Cycas the carpels Plate XV, are ordinary leaves, with ovules upon their margin. A pistil is usually formed by more than one carpel. The carpels may be arranged like leaves, either at the same or nearly the same height in a verticil, or at different heights in a spiral cycle. When they remain separate and distinct, thus showing at once the composition of the pistil, as in Caltha, Ranunculus, Hellebore, and Spiraea (fig. 202), the term apocarpous is applied. Thus, in Crassula rubcns (fig. 172) the pistil consists of five verticillate carpels o, alter nating with the stamens e. In the Tulip-tree and Ranun culus (fig. 254) the separate carpels are numerous and are arranged in a spiral cycle upon an elongated axis or recep tacle. In the Raspberry the carpels are OH a conical