THE VITAL PROPERTIES OF THE CELL 161 



sides of the disc, a starch granule is situated. When this is small, 

 it is completely covered with a thin coating of the substance of 

 the amyloplast ; when it is somewhat larger, only the side turned 

 to the amyloplast is so coated. Further, a concentric stratification 

 may occur; under these conditions the hilum, which is surrounded 

 by the concentric layers, is situated near the surface, which is 

 turned away from the amyloplast. Hence the layers on this sur- 

 face are very thin, becoming gradually thicker and thicker as they 

 approach the starch-forming corpuscle, which is only natural, 

 since they grow out of it, and are formed by it. Frequently a 

 rod-shaped crystal of albumen may be seen embedded in the 

 substance of the amyloplast, on the surface which is turned away 

 from the starch granule. 



Now since starch, as has been already mentioned, can only be 

 produced synthetically in the green portions of plants, theae white 

 amyloplasts cannot be regarded as its true places of origin. It 

 is much more likely to be true that they have obtained the starch, 

 in a soluble form, probably as sugar (Sachs), from those places 

 where assimilation occurs, so that their only function is to re- 

 convert this soluble substance into a solid, organised body. 



The chlorophyll granules (Fig. 68) must be 

 closely connected with the starch-forming 

 corpuscles, since the latter may be converted 

 directly into them this occurs when chloro- 

 phyll under the influence of sunlight develops 

 in them. In such a case the amyloplasts turn 

 green, increase in size, and part with their 

 starch granules, which become dissolved. In 

 addition, chlorophyll granules are formed otFunariahygrometrica, 

 from the colourless trophoplasts, which are ^ th in yesting con- 



r r . . dition and undergoing 



developed at the growing points in the torm division, (x 5\o-. after 



of undifferentiated corpuscles; finally they 



multiply by division in the following manner 



(Fig. 68) : to start with, their substance increases in size, and 



they elongate themselves ; they next become biscuit-shaped, and 



finally divide into two equal portions. 



The chlorophyll granules consist of two substances : a ground 

 substance, which reacts like albumen, and a green colouring matter 

 (chlorophyll), which saturates the stroma. This may be extracted 

 by means of alcohol, when it is seen to be distinctly fluorescent, ap- 

 pearing green with transmitted, and bluish red with reflected, light. 



