THE VEGETABLE KINGDOM. 481 



order to penetrate more deeply, it became necessary to re- 

 nounce these two hypotheses. 



Knight and Dutrochet, seeing that when seeds are made 

 to grow in the buckets of a wheel set in motion by mecha- 

 nism the rootlets always tend outwards and the stems in- 

 wards, concluded that the divergence of these organs was 

 owing to the influence of terrestrial gravitation. 



It was also thought that the direction of the roots was 

 due to their trying to escape the light, but by means of 

 experiments, in which suspended plants were lighted from 

 below, it was ascertained that these organs directed them- 

 selves towards the light. Hence this hypothesis really ex- 

 plains the cause of the direction which plants take no bet- 

 ter than the others. 1 



In proportion as the embryo is developed, the cotyledons, 

 as Malpighi remarked, become filled with vessels, the office 

 of which is to secrete the first nutritive fluids of the young 

 plant ; for this could only find in the ground food too active 

 or too coarse for its yet undeveloped tissues. Then, when 

 these vegetable mammae, as Bonnet called them, have ac- 

 complished their function, and when the roots are vigorous 

 enough to nourish themselves, the part of these organs be- 

 ing played out, they fade and fall. 



Such is the last phase in the evolution of the young 

 plant. 



At the same time that these different vital actions are 

 carried on, the germination is the theatre of important 



1 M. Blondeau, in a memoir read before the French Academy, stated that 

 exposure of some seeds to an induced electric current has the effect of making 

 the stem and leaves grow down into the earth, while the roots come up and take 

 their place. Tit. 



