102 PLANT ANATOMY. 
when they lie close beside each other, become flattened polyhe- 
drically, without, however, coming in contact, for the reason 
that they are provided with a thin membrane of protoplasm, 
They are the organs in which the most important process of 
plant life is effectuated, viz., the assimilation of carbonic acid 
under the influence of light, with the formation of organic or 
carbon compounds. Only. organs containing chlorophyll are 
capable of effecting this change. Indeed, we also find in the 
chlorophyll granules an abundant accumulation of assimilation 
products, and especially starch (Fig. 33, 0, c,d). Ifa leaf of 
the peppermint, after the coloring matter has been extracted by 
Fie. 33.—a, Chlorophyll granule, the sponge-like structure indicated by punctations ; 
5, c, d, inclosures of starch in the chlorophyll granule ; e, a cell with chlorophyll gran- 
ules located along the wall (Tschirch). 
alcohol, is placed in iodine-water (see Micro-chemical Reagents), 
it assumes at one a bluish-black color ; every chlorophyll gran- 
ule contains some starch granules of a black color (see the 
iodine-starch reaction). oe P 
The chlorophyll granules always lie imbedded in the proto- 
plasm-sac, on the inner wall of the cell, and shrink by the 
_ contraction of the sac, by the addition of reagents, or by the 
_ death of the cell. Since the fundamental mass of the chlorophyll 
granules is very soft, many of these flow together by this process 
____ to form larger masses. Thus in drugs (green leaves and stems) 
