THE PATH OF EVOLUTION 



up entirely by the oil, the alcohol retaining a yellow 

 substance Xanthophyll dissolved. This is thought, 

 however, by some to be a product of decomposition 

 of the chlorophyll. It is the cause of the yellow 

 coloring of the foliage in the autumn. The green 

 substance contains, in combination, beside the hydro- 

 carbons, about two per cent, of earthy and alkaline 

 salts.* Iron is also essential. If it is absent in the 

 nourishing fluids, the leaves are colorless, becoming 

 green only when it is supplied. (Pierer's K. L., 1889.) 

 The green substance constitutes only a small portion 

 in weight of the corpuscles. After extraction by 

 alcohol the corpuscle is colorless, but not appreciably 

 diminished in size. 



The presence of warmth, and especially of sun- 

 light, is requisite for the production and the func- 

 tional life of the Chloropyhll bodies. They first 

 appear as colorless or yellowish granules in the 

 young newly-formed cells embodied in the plasmo- 

 dium, becoming rapidly green in the light of day. 

 A temperature of at least 40 degrees F. is requisite 

 for their development. Their functional activity 

 increases with heat, though the too intense action of 

 the solar rays is destructive. The green corpuscles 

 are alive, surrounded with the protoplasm in which 

 they group themselves towards the exterior surface 



* Kerner Von Marilaun. Pflanzenleben. B. 1. S. 345. 

 242 



