CHAP, ir.] CHEMISTRY, ETC., OF PLANT LIFE. 



63 



Chlorophyll grains are always imbedded in the proto- 

 plasm from which indeed they are formed, their forma- 

 tion commences while the cells are still in darkness, for 

 example in young leaves before the expansion of the leaf- 

 bud, and continues until they assume the sickly yellow 

 colour presented by plants that have developed in the 

 dark, as under logs or stones ; for their further develop- 

 ment, that is, the formation of the bright green colour, 

 two conditions are necessary, exposure to light, and the 



Fig. 19. Cell from the leaf 

 of Vallisneria spiralis. The 

 nucleus, k, and chlorophyll- 

 grains, cl, are seen imbedded 

 in the parietal layer of proto- 

 plasm. The arrows indicate 

 the direction of the currents 

 of protoplasm. (Highly mag- 

 nified.) 



presence of iron in solution in the cell-sap. The chloro- 

 phyll-grains do not fill the cell, but are arranged 

 in the protoplasm just under the cell-wall, the central 

 portion of the cell being filled with sap or the raw 

 material ready for undergoing assimilation. 



The first observable product of assimilation is starch, 

 which makes its appearance as small colourless grains in 

 the chlorophyll-grains. Examined under the micro- 

 scope, starch-grains present a characteristic appearance. 



