CHAP. V. FUNCTION OF REPRODUCTION. 26? 



at the progress which this inquiry has already made, 

 although much yet remains to be done before a complete 

 elucidation of all points can take place. 



(263.) Granules With a lens which magnifies 



about 300 times in linear measure, the form of the gra- 

 nules in the fovilla may be clearly distinguished. Whilst 

 still in the pollen tubes they are often in motion, like 

 the globules in the stems of the Chara (art. 194.). A few 

 larger molecules are found dispersed among them, appa- 

 rently of an oleaginous nature. In the same species 

 all the granules are nearly of the same size and shape, 

 but they differ in different species. They are always 

 more or less spheroidal or cylindrical. They are cer- 

 tainly to be considered as the direct agents employed in 

 securing the fertility of the ovules. 



(26'4.) Action of the Stigma. When the grains of 

 pollen fall upon the stigma, they become attached to it 

 by means of a glutinous exudation with which it is 

 covered. No immediate action takes place, and the 

 grains are not violently exploded with the pollenic 

 tubes as when they are placed in water ; but after they 

 have remained for a few hours, and in some cases even 

 for a few days on the stigma, each grain protrudes one 

 or more delicate pollenic tubes which penetrate be- 

 tween the vesicles of the cellular tissue of the stigma 

 (fig. 16'l.a). These tubes increase rapidly in length, 

 growing as it should seem by 

 meansof thenourishmentwhich 

 they derive from the granular 

 matter abounding in the inter- 

 stices or intercellular passages 

 between the vesicles of the 

 style. In some cases if not 

 in all, the pollen tubes become 

 extended down the whole length 

 of the style, and penetrate into the cavity of the 

 ovarium, where they run along the surface of the pla- 

 centa, and surround the ovules. At (6) we have the 

 section of a stigma on whose surface are numerous pol- 



