348 Mineral Nutrition of Plants 



As stated, the onset of blossoming or anthesis is marked by an appar- 

 ently simultaneous reduction in absorption by roots, an internal shift 

 in water balance (//, 37, 40, 56, 58, 63, 64, 107, 121, 122, 127), and redis- 

 tribution of both organic and inorganic nutrients (28, 73, 89, (jo, 127). 

 At the present time it seems that the foregoing phenomena are all the 

 results of some as yet indefinitely defined regulatory or causative fac- 

 tors. We already have some evidence, however, that they are at least 

 associated with, if not caused by, increments in growth substances at 

 reproductive loci within the plant following syngamy {144, 145, 150). 



During anthesis, the carbohydrate supply of roots and their rates of 

 absorption commonly fall to low levels (//, 25, 40, 4], 61, 78, 102, 137). 

 The inadequacy of root carbohydrates at this period has frequently 

 been advanced as the cause of their low absorptive activity (40). As 

 already noted, however, recent data indicate that the organic reserves 

 of the root function jointly with growth substances in absorption and 

 root enlargement. 



In liquid and gravel culture experiments in which entire plants in- 

 cluding roots and the nutrient solution have been analyzed, there is 

 evidence of transitory excretion of certain mineral elements during 

 anthesis {4, 22, 38, 47, 5/, 147). Nitrogen and potassium especially often 

 increase temporarily in the nutrient medium (5/). The recent work of 

 Cailachian (23) on nitrogen in relation to flowering indicates that there 

 are three categories of plants — namely, those in which nitrogen acceler- 

 ates, delays, or has no effect on flowering (144). 



During anthesis, lower leaves show a rapid acceleration in loss of 

 water (82, 83, 121) and organic reserves (83), a trend which subse- 

 quently reaches the extreme of protoplasmic disintegration and transfer 

 of such cellular residues to reproductive organs and to younger vege- 

 tative tissues. In the early stages of this trend, loss of water is progres- 

 sive despite appreciable increments in osmotic values of press sap. 

 Hydrolysis of insoluble organic reserves of lower leaves is a conspicuous 

 phenomenon at this time (2), yet the resulting rise in the osmotic pres- 

 sure of tissue fluids is usually unable to arrest water loss (//, 83, 103, 

 127). The inference follows that factors other than osmotic pressures 

 serve in regulation of the water balance of tissues (83, 127). Numerous 

 studies on the drought resistance of plants have shown their extreme 



