EXPERIMENTAL 

 PLANT PHYSIOLOGY 



SECTION I 

 THE FOOD OF THE PLANT 



CHAPTER I 

 I. THE COMPOSITION OF THE SOIL 



Introductory. — The fact that as a plant develops it 

 increases in weight, is one that needs no demonstration. 

 The oak tree is obviously heavier than the acorn from 

 which it grows. This increase in weight must have 

 been caused by absorption of food-material on the part 

 of the plant. Now the only available sources from 

 which a plant can absorb food are the soil and the air. 

 It is necessary to determine, therefore, whether the 

 plant takes in food from one or both of these sources, 

 and, further, what is the nature of the food taken in. 



The Composition of the Soil. — The soil is composed 

 of grains formed from the breaking down of rocks, to- 

 gether with a varying amount of humus or decaying 

 animal and vegetable matter. The particles are loosely 

 held together, and the spaces between are filled with 

 air and water. 



As a great many of the substances contained in the 

 soil are soluble in water they pass into solution ; thus 

 the water ceases to be pure and becomes a solution of 

 various salts. 



An analysis of this solution is beyond the scope of 

 this book, and we must be content to use the results 

 given to us by chemists. 



