FLOWERS AND THEIR WORK. 



223 



255. The Crynecium or Pistil is the collective term applied to the 

 carpels present in a flower. In its simplest form the pistil consists of 

 a single carpel, as in the Bean. Such a carpel corresponds to a leaf 

 bearing ovules on its margins (Fig. 73), a condition in which the carpels 

 of the Gymnospermous plant Cycas remain to the present day. We 

 might suppose that as the higher flowering plants developed, the two 

 halves of the carpellary leaf became folded longitudinally, and that 

 their margins grew together along a line known as the ventral suture, 

 which bears a double row of ovules on the two margins of the leaf. 



Fig. 73. Carpellary 

 Leaf with Marginal 

 Ovules. 



Fig. 74. The Monocarpellary 



Pistil (e.g. Bean, Pea). 

 A, Entire ; B, Transverse section 

 of Ovary; C, Will indicate 

 method of folding. 



The purpose of this change is immediately obvious, for the young 

 ovules are now protected within a hollow chamber known as the ovary 

 (Fig. 74), which is formed from the swollen basal portion of the carpel. 

 The apical portion of the latter forms a slender prolongation of greater 

 or less length, the style, which usually contains a central canal com- 

 municating with the cavity of the ovary, but may be composed of loose, 

 solid tissue with no definite central cavity. The stigma, or apical 

 portion of the style, is usually swollen and covered with hairs (stig- 

 matic papillae). The stigma forms the receptive surface for the pollen. 

 The dorsal suture of the carpel corresponds to the midrib of a leaf ; 

 the cushion of tissue along the ventral suture, from which the ovules 

 arise, is known as the placenta. In the Water-lily, Flowering Rush, 

 and a few other plants, the ovules are scattered all over the inner 

 surface of the carpels. 



The flower of Buttercup or Rose contains several free simple carpels, 

 and the pistil is therefore termed apocarpous. When several carpels 

 are present in a flower, they are often united to form a compound or 



