170 SOME RECENT RESEARCHES IN PLANT PHYSIOLOGY 



ing as the sugars are increased by photosynthesis, by 

 translocation, or by hydrolysis of insoluble carbohydrates, 

 or are reduced by respiration, translocation, or by con- 

 structive metabolism. 



The pressures found in the leaves almost invariably 

 exceed those of the roots. It must, however, be remem- 

 bered that the values recorded in the tables are all calcu- 

 lated for 0, whereas the actual pressures are higher owing 

 to the plant tissues being normally at 10 to 20. Thus 

 if in a particular instance the sap of the leaves and roots 

 had an identical freezing-point, yet if the former were 

 warmer than the latter they would possess a higher 

 pressure. 



Among the highest pressures are those of fruits, in 

 which when ripe all the available polysaccharides have 

 been converted into sugar. 



Pressures of considerable magnitude are also met with 

 in subterranean storage organs of various kinds, especially 

 in those in which soluble reserves accumulate. 



