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CO 



UNIVERSITY OF CALIFORNIA PUBLICATIONS 



IN 



AGRICULTURAL SCIENCES 



Vol. 1, No. 11, pp. 341-394, plates 5-15 January 31, 1917 



INFLUENCE OF THE COMPOSITION AND 



CONCENTRATION OF THE NUTRIENT 



SOLUTION ON PLANTS GROWN 



IN SAND CULTURES 



BY 

 AETHUR HUGO AYRES 



INTRODUCTION 



Since the recognition of the fact that the mineral content of 

 the plant body is derived from the mineral constituents of the soil, 

 the part which the soil solution takes in the nutrition of the plant 

 has been the subject of numerous investigations by chemists, plant 

 physiologists, and soil scientists, who have made large contri- 

 butions to our knowledge in this important field. The early 

 investigations of Knop and other plant physiologists showed 

 conclusively that the elements which are essential to plant growth 

 are carbon, hydrogen, oxygen, nitrogen, sulphur, phosphorus, 

 potassium, magnesium, calcium, and iron. As most of this work 

 was done before the development of the new chemical and physi- 

 cal theories, in regard to solutions in particular, the problems 

 dealing with the absorption of these elements remain for expla- 

 nation in the light of this new knowledge. The modern period 

 of research in this field has thus been characterized bj'^ an in- 

 tensive study of the absorption of nutrient elements by the plant. 

 The earlier conceptions, which had a marked tendency to link 

 each element with some specific physiological process or with the 

 development of some morphological part of the plant, have been 



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