l66 PLANT LIFE. 



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

 tinued absorption depends u]ion 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, {b) proteids. 



229. I. Carbohydrates. — 'J"he jirocess by which carbo- 

 hydrates are produced is czWtA phatosYntax. The conditions 

 under which photosyntax occurs are three : [a) the presence 

 of chlorophyll, (b) the action of light, and { c j the presence 

 of potassium sails. 



230. (i?j Chlorophyll. — Chlorophyll, as has been shown 

 in Tart I, sometimes colors the whole proto[)lasia of the cell, 

 but is more conunonly 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 chloropihyll 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 chloroi>hyll, be examined with a spectroscope, 

 seven dark bands appear in jilace of certain of the colored 

 rays, because these lia\e been stopped by the chlorophyll 

 (fig. [ 73). ( )ne absor]iti(m band lies between the red and the 

 orange ( 3-9 of scale, fig. i 73), another in the orange (11-14), 

 the third, fainl, in the yellow (17-20), the fourth at the 

 edge of the green (30-32), while the filth (S3-73). sixth 

 (75-93), and se\'enth (94-100) bands occuiiy most of the 

 blue and \iolet. These last three blend into one exlremcly 

 broad band, except when the light passes through very small 

 i|uantitics of chloro])hyll. 



231. (/') 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 



