W. F. Loe hiving 349 



sensitivity to water shortages during flowering {2J, 68, 116, i2g). Even 

 if plants survive drought at the flowering stage, they seldom show a 

 normal course of development thereafter. 



Smirnov {127) and his associates have shown by a series of ingenious 

 experiments that water loss and hydrolysis of organic reserves occur 

 simultaneously with a reduction in the amount of hydrophilic colloids 

 in vegetative tissues. Smirnov stresses the "salting out" effect of mineral 

 nutrients upon organic colloids and the resultant reduction in water 

 retentivity by colloids after precipitation. Precipitation of cell colloids 

 is evidently accompanied by liberation of previously absorbed enzymes 

 and a simultaneous increase in their hydrolytic action. During this 

 period, there also occur marked changes in pH of tissue fluids; such 

 alterations may be additive to the effects of colloid precipitation in in- 

 creasing the hydrolytic action of enzymes. Many investigations provide 

 evidence of marked reduction in the rate of photosynthetic activity 

 during the period of rapid hydrolysis of organic reserves (//, 148). 



Relatively low levels of tissue moisture and hydrolysis of organic re- 

 serves in lower leaves frequently involve living protoplasm (46, 49, 99, 

 108, 123, 124), and, once the protoplasmic components of such tissues 

 begin to undergo hydrolysis, they usually become incapable of renewed 

 synthesis even upon amelioration of the water and nutrient supply 

 (Sj, 104, 132). This observation is usually offered as the explanation of 

 the early death and abscission of lower leaves of plants in the repro- 

 ductive phase. Mothes (8y) has shown the dependence of protein syn- 

 thesis upon internal oxygen tension, and a reduction in rate of protein 

 formation commensurate with the decline in the rate of photosynthesis. 

 Smirnov's data {i2j), in turn, show a correlation between the rates of 

 respiration and protein synthesis (49). It thus appears that photosyn- 

 thetic oxygen favors protein formation by acceleration of aerobic oxi- 

 dation of carbohydrates. The resultant energy is important to the re- 

 duction of nitrates as well as to the union of nitrogen with carbo- 

 hydrate derivatives in amino acid synthesis. Smirnov points out that 

 in the early life of annuals, protein synthesis parallels, and hence is pre- 

 sumably dependent upon, the concentration of hexose sugars. With the 

 onset of reproduction, however, protein production ceases to be propor- 

 tional to the soluble sugar content but parallels the rate of foliar res- 



