The Plant as a Metabolic Unit 243 



tern indirectly modify the rate of intake from the soil solution 

 and the problem of translocation requires investigation with this 

 in mind. There is need of further knowledge of carbon dioxide 

 production by root cells, as influenced by soil aeration, soil tem- 

 perature, carbohydrate synthesis and translocation, and related 



factors. 



The discussion may be appropriately closed by emphasizing 

 again the general view that problems of the soil-plant system 

 cannot be solved without the aid of patient and laborious experi- 

 mentation under conditions which permit the requisite control 

 of the plant's environment and the quantitative measurement of 

 processes or of their end products. Such researches are indis- 

 pensable to the development of scientific knowledge in the field 

 of geobotany or of practical agriculture. 



Summary 



The metabolic activities of the plant are reviewed with special 

 reference to the absorption of mineral elements. Methods of con- 

 trolled experimentation are considered and certain results cited. 

 In connection with the process of solute accumulation, emphasis 

 is placed on the supply of carbohydrates available to root cells, 

 and on the temperature and oxygen-supplying power of the root 

 medium. Relations of transpiration to absorption of mineral 

 solutes, relation of absorption of these solutes to plant bufiFer 

 systems, and other interrelations of the soil-plant system are 

 discussed. 



