258 



WILLIAM E. LAWRENCE 



EXPLANATION OF THE CHART 



It is unnecessary to give a detailed description of every reaction 

 shown in this chart. The reader will need only to follow through 

 a few of the more important processes to secure an idea of its mani- 

 pulation. Certain reactions which are most evident or most 

 essentiallj^ connected with the life of the plant, and certain sub- 

 stances and energj^ forms which are met with in greatest amounts 

 are indicated, respectively, by broad connecting lines and hea\^' 

 lettering. The narrower lines and lighter lettering signify the 

 minor processes, substances and energy forms, chiefly from a 

 quantitative point of view. This distinction is of course arbi- 

 trary, but the use of a greater number of gradations would lead to 

 confusion rather than to clearness. 



It will be observed that the processes which are primarily in- 

 cluded in constructive and destructive metabolism are arranged in 

 a closed circle and read in a clockwdse direction. The sequence 

 of the various processes, their dependence upon one another and 

 their relation to those which follow are indicated by the arrows. 

 In this way may be seen almost at a glance, not only the contribu- 

 ting factors and resulting products or processes, but also other alter- 

 natives or minor Unes of activity. While it requires considerable 

 study to trace all the various relations, it is at least readil}^ ob- 

 served that no process is in any way independent of all others, a 

 point which is of exceedingly great fundamental * importance. 

 The interaction of all these processes constitutes that very delicate 

 and automatic system of material changes called vitality, which 

 is manifested by the production and very existence of the plant. 



Since all chemical and physical changes depend fundamentally 

 upon temperature, and since the plant body and its surroundings 

 always tend to come into (and indeed approach), temperature 

 equilibrium, it is clear that every physiological process which ren- 

 ders kinetic energy potential must be accompanied by absorption 

 of heat, either from the environment or from some region of the 

 body in which a reverse process is liberating heat. Likewise, the 

 heat liberating processes are accompanied by a transfer of heat 

 either to the exterior or to other regions. To bring these consider- 



