84 EXPERIMENTAL PLANT PHYSIOLOGY 



the air during the early stages of its growth, since this 

 source of supply is not available until some green 

 leaves have unfolded. 



On the other hand, the substances dissolved in the 

 water, which constitute the food-supply from the soil, 

 are available to the plant from the beginning of its 

 growth. Whether or no these dissolved substances 

 are necessary for germination can be shown by the 

 following experiment. 



Experiment 52 



Aim. — To find out whether a seed requires food from 

 the soil in order to begin to grow. 



Method. — Three broad-beans are planted. One is 

 put into earth, one into cocoanut fibre, and the third is 

 suspended over water in a corked bottle so that it is 

 in a damp atmosphere. The bean that was planted in 

 cocoanut fibre is watered with distilled water. 



Thus one only of the three seeds is provided with 

 mineral food. 



Observations.— All three seeds begin to grow. 



Inference. — Food from the soil is not necessary in 

 the initial stages of growth. 



It has thus been proved that a seed can germinate 

 without nourishment either from air or soil. This does 

 not imply that growth is possible without food, although 

 it may appear at first sight as if it were a case of a 

 "building-up" without a "breaking-down." But such 

 a case is impossible. The growth of the seedling neces- 

 sarily involves an expenditure of energy ; and this 

 energy must be constantly renewed or the seedling will 

 die. Somewhere "potential " energy must be converted 

 into "kinetic " energy. Or, in other words, assimilated 

 food substances must be broken down so that energy 

 necessary for the growth of the seedling can be liberated. 



Where then does the seedling obtain this assimilated 

 food, since it cannot manufacture any for itself ? 



In answer to this question it may be said that the 



