1917] Ayres: Nutrient Solution on Plants Grown in Sand Cultures 343 



sitioii of the solution. In decided contrast to the evidence cited 

 above, we have the investigations of Hall, Brenchley, and Under- 

 wood," who conclude, on the basis of their results with barley 

 plants grown in a standard solution of four different concen- 

 trations, that "the growth made by plants in the soil solution is 

 in the main determined by the amount of plant food they con- 

 tain," and that "the concentration of the nutrient solution 

 within certain wide limits, irrespective of the total amount of 

 the plant food available, is a factor in the rate of plant growth 

 which varies directly though not proportionally with the strength 

 of the solution in the particular nutrient or nutrients limiting 

 the growth." The experiments of Shive* are of considerable 

 interest in this connection. Wheat was grown in solutions of 

 three different total concentrations, 0.1, 1.75, and 4.00 atmos- 

 pheres, in terms of possible osmotic pressure. The solution used 

 was tlie three-salt solution first used by Birner and Lucanus" 

 containing Ca(N0.,)2, MgSO^, and KH.PO,. All possible sets 

 of proportion of these salts were included for increments of 

 change equal to one-tenth of the total possible osmotic pressure. 

 As judged from the extensive quantitative data collected, Shive 

 concludes that the growth of wheat plants in solutions of any 

 given salt proportion is determined by the concentration of the 

 medium. 



In the course of some experimental work concerning the drop- 

 ping of flowers by Fj species-hybrids of Nicotiana}'^ it seemed 

 desirable to grow a considerable number of plants in sand cul- 

 tures which would vary widely both as to the principal nutrient 

 elements, nitrogen, phosphorus, and potassium, and as to the 

 total concentration of all of the nutrient salts. The marked 

 influence of the nutrient factors upon the growth of the plant 

 has afforded an excellent opportunity for a somewhat detailed 

 study of the influence of the composition and concentration of 

 the nutrient solution upon the growth of one of the higher seed- 

 plants of herbaceous character. 



7 Hall, Brenchley, Underwood, Jour. Agric. Sei., vol. 6, pp. 278-301, 

 1914. 



8 Shive, Physiol. Ees., vol. 1, pp. 327-396, 1915. 



9 Birner and Lueanus, Landw. Versuehsstat., vol. 8, pp. 128-177, 1886. 

 loGoodspeed and Ayres, Univ. Calif. Publ. Bot., vol. 5, no. 9, 1916. 



