44 FOOD OF THE VEGETATING PLANT. CHAP. I. 



even when totally immersed so as that no other 



food seems to have access to them ; does it not 



Thought follow that water is the sole food of plants, the soil 



solelfood being merely the basis on which they rest ; and 



of plants. the rcce p tac i e O f t h e i r food ? This opinion has had 



many advocates ; and the arguments and experi- 



ments adduced in support of it were at one time 



thought to have completely established its truth. 



It was indeed the prevailing opinion of the seven- 



teenth century, and was embraced by several phi- 



losophers even of the eighteenth century ; but its 



ablest and most zealous advocates were Van Hel- 



mont, Boyle, Du Hamel, and Bonnet, who con- 



tended that water, by virtue of the vital energy of 



the plant, was sufficient to form all the different 



substances contained in vegetables. 



Theopi- Van Helmont planted a Willow weighing 50lb. 



nioncoun- . ... 



tenanced in an earthen vessel containing a known quantity 

 ^ eart ^ which had been previously dried in an 



of Van oven. He moistened it with distilled water, or 



Helmont, 



with rain water, and took care to prevent any ac- 

 cession of other earth. At the end of five years 

 the plant was taken up and weighed. Its weight, 

 together with that of all its leaves, was l6Q4-lb. 

 and the weight of the earth, only two ounces less 

 than at first, giving an accession of JJQ-flb., which 

 is to be accounted for only from the water with 

 which the earth was moistened. Hence it was con- 

 eluded that water is the sole food of plants ; the 

 two ounces of earth lost being regarded as bearing 



