CHAPTER I 



HISTORICAL 



That admirable naturalist, Aristotle, knew the physiology of 

 animals very well and it was through them that he tried to 

 understand plants and their Ufe. The latter draw from the 

 soil their nutrition, which is so well dissolved and digested in 

 the water that it has no more modification to undergo. The 

 vegetable organism may therefore be extremely simple, or 

 may indulge in the luxury of green leaves, the sole purpose of 

 which is to protect the fruits against the burning sun. 



In the seventeenth century, a Dutchman, Van Hehnont, 

 convinced that the plant was nourished not with soil, but 

 with water, made the following experiment. After filling a large 

 pot with 200 lb. of well-dried earth, he planted in it a willow 

 branch weighing 5 lb., watered it regularly with rain-water and 

 placed a cover over the surface of the soil to prevent dust 

 being added to it. At the end of five years, the willow had 

 grown and weighed 169 lb. The earth was dried again and 

 weighed; only 2 ounces had been lost. His conclusion was 

 that *'it is not with soil that plants are nourished but with rain- 

 water, from which they elaborate all their substance." 



Towards the end of the eighteenth century, the ItaUan, 

 Malpighi, discovered the importance of the leaves. He had 

 observed that a young plant will not germinate if its cotyledons 

 are suppressed. After giving much thought to this experiment, 

 he concluded that the capital transformation — the assimilation 

 or, more precisely, the digestion of the substances absorbed 

 by the roots — is made in the cotyledons or leaves to which 

 the plant transports these substances through the vessels and 

 where, with the help of the sun, the raw material is trans- 

 formed into Uving matter. 



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