Hoagland — 114 — Plant Nutrition 



applicable, an especially high calcium concentration 

 would be desirable. 



In the course of the investigation now under dis- 

 cussion, nutrient absorption studies were carried out, 

 with several suggestive results. Some of these ex- 

 periments consisted in growing plants for a suitable 

 period under favorable conditions and then subjecting 

 the plants for short periods to solutions of various pB. 

 values. At the most acid reactions Ca was not ab- 

 sorbed by the plants and, in fact, loss of this element 

 occurred from the roots to the solution. From solu- 

 tions of otherwise similar composition those with the 

 higher pH values permitted more calcium absorption 

 to occur. On the other hand, at markedly alkaline 

 reactions, little or no phosphate was absorbed. The 

 full explanation of this effect is not now at hand, 

 although several suggestions are under examination. 

 (See plate 23 and text fig. 33). 



As a special feature of nutrient solution technique 

 it is well to keep in mind certain characteristics of 

 the two forms of nitrogen that may be supplied, 

 nitrate nitrogen and ammonia nitrogen. The ammonia 

 nitrogen is absorbed as a rule so much faster than 

 the associated anions that the tendency is for the 

 solution to increase in acidity; the converse is gen- 

 erally, although not invariably, true of the nitrate ion. 

 As Trelease and Trelease (1935) have pointed out, 

 a convenient rough automatic control of pYi of a 

 solution during plant growth can sometimes be gained 

 physiologically by supplying a suitable mixture of 

 ammonia and nitrate nitrogen. We have had some 

 success with this method in culture experiments on 

 tomato plants. 



Aeration of Nutrient Solutions : — With this brief 

 survey of nutrient solutions with respect to their 

 content of ions before us, permit me to return once 

 more to the question of the aeration of roots. The 

 potentiality for excellent growth and yield of fruit by 



