238 SOIL CONDITIONS AND PLANT GROWTH 



There has been much controversy as to the effect of con- 

 centration of the nutrient solution on plant growth. The 

 relationship is curiously elusive : at first sight it appears a 

 most simple thing to ascertain. The difficulty is to change 

 the solutions sufficiently often to prevent complications due to 

 exhaustion of essential nutrient substances. 



Breazeale ($\a) concluded from his experiments that 

 small variations in concentration of the nutrient medium are 

 without effect on plant growth ; this view is accepted by 

 Whitney and Cameron and in this country by Stiles. 1 It is 

 vigorously controverted by Hall, Brenchley, and Underwood 

 (\2\c\ see also 54^), who maintain that within certain limits 

 the plant growth is affected by and increases with the con- 

 centration, although recognising that the differences become 

 less as the solutions are more frequently changed. Hoagland 

 and Sharp (136^) also find that growth increases with increas- 

 ing concentration up to a point, beyond which no further 

 growth is obtained : absorption of nutrient salts still continues, 

 however. Some of their results with barley, after two days 

 growth, are given in Table LXIII. 



TABLE LXIII. TRANSPIRATION AND GROWTH OF BARLEY IN SOLUTIONS OF 

 DIFFERENT CONCENTRATIONS. HOAGLAND AND SHARP, 136^. 



Adequate concentration of nutrients is of great importance 

 in the early stages of plant growth : in later stages high 

 concentration is less necessary and may be undesirable. 2 



1 Annals of Botany, 1915, 29, 89. 



2 See also J. S. Burd, Journ. Ag. Research, 1919, 18, 51-72. 



