lOO THE ORIGIN AND EVOLUTION OF LIFE 



also extremely ancient. Near the base of the Archaean rocks^ 

 graphites, possibly formed from fossilized plant tissue, are 

 observed in the Grenville series and in the Adirondacks. The 

 very oldest metamorphosed sedimentaries are mainly composed 

 of shales containing carbon which may have been deposited by 

 plants. 



As a reservoir of life energy which is liberated by oxidation, 

 hydrogen exceeds any other element in the heat it yields, 

 namely, 34.5 calories per gram, while carbon yields 8.1 calories 

 per gram.- Since the carbohydrates constitute the basal 

 energy-supply of the entire plant and animal world, ^ we may, 

 with reference to the laws of action and reaction, examine the 

 process even more closely than we have done above (p. 51). The 

 results of the most recent researches are presented by Wager:"* 



"The plant organ responds to the directive influence of 

 light by a curvature which places it either in a direct line with 

 the rays of light, as in grass seedlings, or at right angles to the 

 light, as in ordinary foliage leaves." "Of the light that falls 

 upon a green leaf a part is reflected from its surface, a part is 

 transmitted, and another part is absorbed. That which is 

 reflected and transmitted gives to the leaf its green color; that 

 which is absorbed, consisting of certain red, blue, and violet 

 rays, is the source of the energy by means of which the leaf is 

 enabled to carry on its work. 



"The extraordinary molecular complexity of chlorophyll has 

 recently been made clear to us by the researches of Willstatter 

 and his pupils; Usher and Priestley and others have shown us 

 something of what takes place in chlorophyll when light acts 

 upon it; and we are now beginning to realize more fully what 

 a very complex photosensitive system the chlorophyll must 



' Pirsson, Louis V., and Schuchert, Charles, 1915, p. 545. 



2 Henderson, Lawrence J., 1913, p. 245. ^ Moore, F. J., 1915, p. 213. 



* Wager, Harold, 1915, p. 468. 



