THE ESSENTIAL ORGANS THE PISTIL. 



127 



the form and appearance of the grains vary much, and will be 

 spoken of hereafter. The pollen of the Asclepiadaceae and Or- 

 chidaceae, however, has a great peculiarity, in remaining perma- 

 nently coherent into masses, often of a waxy character. In 

 Orchidaceae the pollen-masses or pollinia are either single in each 

 loculus of the anther (as they are in Asclepiadaceae), and then 

 often furnished, as in Orchis &c., with a stalk-like process, called 

 the caudicle (fig. 243), terminating in a gland-like base (retina- 

 culum), by which they readily adhere to the stigma or to foreign 

 bodies, such as insects ; or the pollinia are two or four in each 

 loculus, and devoid of a caudicle ; sometimes the pollinia are nume- 

 rous, and form merely a loose granular mass. 



The external characters of the pollen-graius, their structure, and sub- 

 sequent history will be treated of in the Third Part of this work, as they 

 belong to the microscopic anatomy and the Physiology of Plants. The 

 form of the pollen-grains is generally constant in the same plant ; but 

 great variations are often found within the limits of Natural Orders and 

 sometimes in the same genus, so that, excepting the Orchidacese and 

 Asclepiadaceae, and a few other groups, they are not to be relied on as 

 affording any very useful characters in Systematic Botany. Their size, 

 form, and numbers are apparently in relation to their mode of dispersion 

 by the wind or by insects. 



Fig. 244. Fig. 245. 



Fig. 246. 



The Gyncecium or Pistil. 



Carpels. The central essential organs of flowers, composing the 

 pistil, consist, like the outer parts, 

 of phyllomes or modified leaves ; 

 these constituent leaves are called 

 carpels. The peculiar character 

 of a carpel is, that it produces 

 ovules, the rudiments of the seeds 

 usually upon the margins, but 

 occasionally on other parts of the 

 internal surface. In the G-ym- 

 nospermia these ovules are deve- 

 loped upon the edges or surface 

 of expanded carpels. In the An- 

 giospermia, comprehending the 

 great majority of Flowering 



plants, the carpels are folded up, Fig. 244. simple pistil of Prunu*, consisting 

 either singly (fig. 244) or collec- ^.*t&S! a> the ovary '' c> the 



tively, with the margins turned Fig. 245. The same, 'opened, to show the 



in so as to place the ovules in the F^^^^SS'of the carpel of 



interior Of a hollow Case. The Prunus, showing that the ovule arises 

 Case thus formed, enclosin the --enta at the confluent margins 



