50 STRUCTURAL AND PHYSIOLOGICAL BOTANY. 



402. Nothing is, properly speaking, stigma, except the 

 secreting surface of the style. Nevertheless, the name is 

 often inaccurately applied to mere divisions of the style, as in 

 Labiatse ; or to the hairy surface of undivided styles, as in 

 Lathyrus. 



403. Sometimes the stigmas grow to the face of the anthers, 

 which form themselves into a solid mass; Ex. Asclepias 204 . 

 In this case the styles remain separate. 



404. The pistil is either the modification of a single leaf, or 

 of one or more whorls of modified leaves, 



405. Such modified leaves are called carpels. 



406. A CARPEL is formed by a folded leaf, the upper sur- 

 face of which is turned inwards, the lower outwards; and 

 within which are developed one or a greater number of buds, 

 which are the ovules. 



407. When the carpels are stalked, they are said to be 

 seated upon a thecaphore, or gynophore ; Ex. Cleome, Passi- 

 flora. Their stalk is analogous to the petiole of a leaf. 



408. When the carpels are all distinct, or are separable 

 with facility, they are apocarpous ; when they all grow into 

 a solid body, which cannot be separated into its constituent 

 parts, they are syncarpom. 



409. The ovary is the lamina of the leaf. 



410. The style is an elongation of the midrib (208). 



411. The stigma is the denuded, secreting, humid apex of 

 the midrib. 



412. Where the margins of a folded leaf, out of which the 

 carpel is formed, meet and unite, a developement of cellular 

 tissue sometimes takes place, forming what is called the mar- 

 ginal placenta. 



413. Every such placenta is therefore composed of two 

 parts, one of which belongs to one margin of the carpel, and 

 one to the other. 



414. But although the placenta of many plants appears to 

 derive its origin from the margin of the carpels, it is certain 

 that in many other instances the placenta is a mere deve- 

 lopement of the centre of the flower-bud, and in reality the 

 end of the medullary system. Such a placenta is called 

 central. 



It is not impossible that even marginal placentae may be so in appearance only, 

 and be m reality central. 



