A PHYSIOLOGICAL CHART 



259 



ations into the chart would confuse it by undue complication and 

 has not been attempted. 



The plant's nutrition may be considered as starting with the 

 absorption of the light energy from without and its transformation 

 into the potential form in the process of photosynthesis, which 

 depends — in a material way — chiefly upon CO2 from the air and 

 HoO from the soil. The process results in the production of car- 

 bohydrates and the release of oxygen, the latter either escaping 

 to the air or being compounded with carbon in the respiratory 

 process. The principal product — as far as the plant is concerned 

 — is sugar, as shown by the broad line. The products of photo- 

 sjTithesis may follow several paths through the plant before their 

 final incoiporation into the protoplasm. 



The chief reactions taking place within the plant are shown by 

 arrows which traverse the chart, or by the broad bounding lines 

 that connect the principal processes. Those products which 

 escape from the plant, some of them re-entering, are shown by 

 lighter arrows leaving the chart or running around it; e.g., the 

 O2 arrow from atmosphere to respiration. Throughout the chart, 

 every change invohdng the movement of food from one cell to 

 another is shown by the word transfer, inserted in a broken arrow. 

 \^Tiere the line is continuous, not interrupted by any process, or 

 by the word transfer, it is an indication that the reaction takes 

 place within the cell. 



Because of the wide differentiation in the plant kingdom, it is 

 impossible to make a general scheme which will apply to all plants. 

 In plant evolution, we know that physiological differentiation 

 always precedes morphological change, and that ph^'siological 

 varieties are far more abundant than morphological. For plants 

 which accumulate sugar, the principal path of change would be: 

 sugar-starch-digestion-transfer-accumulation . For protein-accumu- 

 lating plants sugar contributes largely to the formation of pro- 

 teins, it is transferred, accumulated, or assimilated according to 

 the physiological characteristics of the protoplasm in different 

 regions of the plant body or in different periods of the plant's 

 life. There should be as many physiological variations as there 

 are plants in the world. Different physiological conditions should 



THE PLANT WORLD, VOL. 16, NO. 9, SEPTEMBER, 1913 



