1917] Ayres: Nutrient Solution on Plaids Grotvn in Sand Cultures 351 



The effect of increasing the quantity of nitrogen from plant 

 1 to plant 4 is marked in all groups. In every group plant 5 

 is not so tall as plant 4 (pi. 5), hence it would seem that the 

 optimum nitrogen supply for tobacco growing in sand cultures, 

 with height as an index, is somewhere near 0.1 per cent of 

 NaNO^, calculated on the basis of the dry weight of the sand. 



Cm. 



60 70 



Dg. totiil concentration 



Fig. 2. — Graph showing the influence of total concentration upon height 

 in series I. 



There is slight variation in the first three plants of groups A, 

 B, and C, showing that change in the total concentration of the 

 solution within these limits does not affect the characters of 

 the plants to any great extent. This, however, does not apply 

 to group D, in which the total concentration is low (1.16 to 

 4.14 g.), for plants 2 and 3 are far superior to the corresponding 

 plants of the other groups, although the nitrogen content is 

 exactly the same. When the nitrogen content is at or near the 



