114 THE NUTRITIVE FUNCTIONS. 



itself, in fact, in the vitally active cells on the exterior 

 surface of plants which are exposed to .the light, and is 

 wholly absent from the roots and from the interior of the 

 stem, to which the light cannot gain access. Chlorophyl 

 exists in the cells, in the form of separate or united gra- 

 nules, which remain either stationary and united to the 

 cell walls, or float freely in the fluid contents of their cavities. 

 These granules are usually of a globular form, and may be 

 readily distinguished in the cells of the liverworts and 

 mosses. They are beautifully apparent in the little lancet- 

 shaped leaves of Selaginella apus, a common but never- 

 theless very interesting moss-like representative of the 

 Lycopodiaceae. 



If the green globules of chlorophyl be subjected to the 

 action of iodine, it will be found that they are composed 

 of one or more starch granules, invested by a gelatinous 

 layer of green coloring matter. This green matter be- 

 comes colored yellow or brown by the iodine, whilst the 

 granules of starch take the blue color which characterizes 

 them, and appear more or less easily and with a purity of 

 tint in proportion to the thinness of the green gelatinous 

 layer in which they are enveloped. That chlorophyl is 

 nothing but fecula viridis* or green starch, is further 

 proved by testing it during the different stages of its deve- 

 lopment. If the young embryo leaves, formed in the au- 

 tumnal buds of the horse-chestnut, be carefully removed 

 from their hybernaculum, it will be found that they are of 

 a pale-yellow color and nearly transparent. If iodine be 

 applied, the chlorophyl granules in their interior will as- 

 sume a deep blue tinge which shows that the gelatinous 



* See "Outlines of Structural and Physiological Botany," by A. 

 Henfrey, page 19. 



