Page:Encyclopædia Britannica, Ninth Edition, v. 4.djvu/152

Rh 142 BOTANY [REPRODUCTIVE ORGANS. receptacle ; in the Strawberry, on a swollen succulent one (fig. 154); and in the Rose (fig. 155), on a hollow one. When the fruit consists of several rows of carpels, the in nermost have their margins directed to the centre, while the margins of the outer rows are arranged on the back of the inner ones. When the carpels are united, as in the Pear, Arbutus, and Chickweed, the pistil becomes syncar pous. The number of carpels in an apocarpous pistil, or the number of separate styles in a syncarpous one, is in dicated in the following way : A flower with a simple pistil or 1 style is Monogynous. 2 separate carpels or 2 separate ) . Di ous&amp;gt; styles ) J 3 carpels or 3 separate styles is Trigynous. 4 carpels or 4 separate styles is Tetragynous. 5 carpels or 5 separate styles is Pentagynous. 6 carpels or 6 separate styles is Hexagynous. 7 carpels or 7 separate styles is Heptagynous. 8 carpels or 8 separate styles is Octogynous. 9 carpels or 9 separate styles is Enneagynous. 10 carpels or 10 separate styles is Decagynous. 12 carpels or 12 separate styles is Dodecagynous. a greater number of carpels or styles is Polygynous. The union in a syncarpous pistil is not always complete; it may take place by the ovaries alone, while the styles and stigmata remain free, the pistil being then gamogastrous (fig. 255), and in this case, when the ovaries form apparently a single body, the organ receives the name of compound ovary ; or the union may take place by the ovaries and styles, while the stigmata are disunited ; or by the stigmata and the summit of the style only. Various intermediate states exist, such as partial union of the ovaries, a3 in the Rue, where they coalesce at their base ; Plate III. and partial union of the styles, as in Malvaceae. The union is usually most complete at the base ; but in Labiatae the styles are united throughout their length, and in Apocynacese and Asclepiadacese the stigmata only. When the union is incomplete, the number of the parts of a compound pistil may be determined by the number of styles and stigmata ; when complete, the external venation, the grooves on the surface, and the internal divisions of the ovary, indicate the number. The changes which take place in the pistil by adhesion, degeneration, and abortion, are frequently so great as to obscure its composition, and to lead to anomalies. Fig. 255. Fig. 256. FIG. 254. Apocarpous compound pistil of Crowfoot (Ranunculus), consisting of numerous separate uni-ovular carpels, arranged in spirals. The flower is V^T* h?V ar P cl co ?sists of ovary, f tyie, and stigma. Two of the W lns &amp;lt;tion below the pistil in the thalamus , f FIax & X &quot;^ Tt consists of five carpels, united sc P arato - Hcnce the fl ^r 1 1 ist.il of the Pea (Pisum satirum) laid open. It consists of a single ig numerous ovules ov, which arc attached to the placenta pi, will nf!,n ll! C i m tU -. rows b - v meails of umbilical cords (funiculi)/ The owcr e, lerm^ofT 81, %L th - CC Iayor8i the OUtcr * Corresponding to the c rfthetea Tt p +i r nei &quot; &quot; corr &amp;lt;=6pondingto the upper epidermis &quot;ike the nknSrtv f 6 ? ^ ye S tll01 C is a sma11 aimmnt of cellular-tissue stigma are marked s a ; alyX is P erfistent - The st y ] e and The pistil is more liable to changes of this kind than any other part of the flower. The carpels are usually sessile leaves, but sometimes they are petiolatc, and then are elevated above the external whorls. This elevation of the pistil may in general, however, be traced to an elongation of the axis itself, in such a way that the carpels, in place of being dispersed over it, arise only from its summit, and the pistil becomes stipitate, or supported on a stalk called a gynophore or thecaphore, .as in the Passion-flower and Dictamnus (fig. 177). Sometimes the axis is produced beyond the ovaries, and the styles become united to it, as in Geraniaceoj (fig. 152) and Umbellifenc. In this case the prolongation is called a carpophore. A Plate VII monstrosity often occurs in the Rose (fig. 145) by which the axis is prolonged, and bears the carpels / in the form of alternate leaves. The ovary contains the ovules. These are attached to The the placenta. This, sometimes called the trophosperm, placenta, consists of a mass of cellular tissue, through which the vessels pass to the ovule. The placenta is usually formed on the edges of the carpellary leaf (fig. 256), and is then said to be of the marginal type. In many cases, however, the placentas are formations from the axis, and are not con nected with the carpellary leaves ; they are then said to bo axile. Some restrict the term placenta to the point of attachment of a single ovule, and call the union of placentas, bearing several ovules, placcntaries or pistillary cords. In marginal placentation the part of the carpel bearing the placenta is the inner or ventral suture, corresponding to the margin of the. folded carpellary leaf, while the outer or dorsal suture corresponds to the midrib of the carpellary leaf. As the placenta is formed on each margin of the carpel it is essentially double. This is seen in cases where the margins of the carpel do not unite, but remain separate, and consequently two placentas are formed in place of one. When the pistil is formed by one carpel the inner margins unite in the axis, and form usually a common marginal placenta. This placenta may extend along the whole margin of the ovary as far as the base of the style (fig. 256), or it may be confined to the base or apex only. When the pistil is composed of several separate carpels, or, in other words, is apocarpous, there are generally separate placentas at each of their margins. In a syncarpous pistil, on the other hand, the carpels are so united that the edges of each of the contiguous ones, by their union, form a septum, or dissepiment, and the number of these septa con sequently indicates the number of carpels in the compound pistil (fire. 257) It is obvious then that each dissepiment Fig. 258. Fig. 259. FIG. 257. Ovary or lower part of the pistil of the Lily (LiUn ii), cut transversely. There are three loculaments, Indicating the union of three carpels, and the ovary is said to be trilocular. The divisions in the ovary, called septa or dissepi ments, are formed by the sides of the carpellary leaves.&quot; Each septum is double, and the number of septa corresponds with the number of the carpels. The ovules are placed collaterally, in pairs, in each loculament, and arc attached ^ to a central placenta, formed by the union of the three ventral sutures. FIG. 258. Diagrammatic section of a quinquelocular or pcntathccal ovary, com posed of five carpels, the edges of which are folded inwards, and meet in the centre. The ovules o are attached to a central placenta, formed by the union of the five ventral sutures. The live partitions, septa, or dissepiments, s, are com posed of the two sides of contiguous carpels. Dorsal suture, I. FIG. 259. Diagrammatic section of a quinquelocular ovary, in which the edges of the carpels, bearing the placentas arid ovules o, are not folded inwards. The placentas arc parietal, and the ovules appear sessile on the walls of the ovary. The compound ovary is unilocular, and the edges of its carpels arc applied to each other in a valvular manner. is formed by a double wall or two laminre ; that the presence of a septum implies the presence of more than one carpel ; and that, when carpels are placed side by side, true dissepi ments must be vertical, and not horizontal. When the dissepiments extend to the centre or axis, the ovary is