1 66 PLANT LIFE. 



but also in permitting the absorption of this gas. Its con- 

 tinued absorption depends upon its continuous removal from 

 the cell sap in the manufacture of carbohydrates. 



228. Anabolism. By this term are designated the con- 

 structive processes of metabolism, by which complex sub- 

 stances are produced from simple ones. These materials 

 belong chiefly to two classes, (a] carbohydrates, () proteids. 



229. i. Carbohydrates.- -The process by which carbo- 

 hydrates are produced is called photosyntax. The conditions 

 under which photosyntax occurs are three : (#) the presence 

 of chlorophyll, ($) the action of light, and (c) the presence 

 of potassium salts. 



230. (a) Chlorophyll. Chlorophyll, as has been shown 

 in Part I, sometimes colors the whole protoplasm of the cell, 

 but is more commonly found only in certain special struc- 

 tures, the chlorophyll bodies. The real work of forming the 

 carbohydrate depends, therefore, upon the protoplasm of the 

 chlorophyll body. The purpose of the chlorophyll is to 

 absorb certain portions of the light which falls upon it. If 

 the light which has been passed through a green leaf, or a 

 solution of chlorophyll, be examined with a spectroscope, 

 seven dark bands appear in place of certain of the colored 

 rays, because these have been stopped by the chlorophyll 

 (fig. 173). One absorption band lies between the red and the 

 orange (3 9 of scale, fig. 173), another in the orange (1114), 

 the third, faint, in the yellow (1720), the fourth at the 

 edge of the green (3032), while the fifth (5373), sixth 

 (7593), and seventh (94100) bands occupy most of the 

 blue and violet. These last three blend into one extremely 

 broad band, except when the light passes through very small 

 quantities of chlorophyll. 



231. (b) Light. --The light absorbed by the chlorophyll 

 furnishes the energy necessary to carry on the work of taking 

 apart the carbonic acid and rearranging the molecules into a 



