8 DISEASE IN PLANTS. 



idea that plant acids were the first products of 

 carbon-assimilation, that some substance, of a 

 slimy nature, was manufactured in the cells of the 

 leaves and thence distributed as the formative 

 material from which the plant constructed its 

 parts. Davy and Boussingault had even surmised 

 that a carbohydrate might be the first-formed pro- 

 duct in assimilation. 



There can be little doubt that Sachs' classical 

 proof, by direct physiological observation and 

 experiment, first brought forward the truth of 

 organic synthesis in the plant in a concrete and 

 convincing form. 



But it did more than that. It laid the founda- 

 tion of the modern physiology of plant-nutrition 

 on ground already prepared by De Saussure and 

 the earlier workers ; for, in addition to emphasis- 

 ing the truth of organic synthesis a truth which 

 had been gradually impressing itself on the world 

 for some years Sachs' discovery showed clearly 

 the real meaning of carbon-assimilation as a pro- 

 cess for obtaining combustible food, which the 

 plant then proceeds to make use of 



Many points were rapidly cleared up at once, 

 or if not explained were at least put into a strong 

 light for further enquiry, and plant-nutrition soon 

 ceased to be the mysterious subject for all kinds 

 of wild conjectures that it had hitherto been. 



The meaning of thin leaves, with numerous 

 stomata and finel}^ ramified or divided vascular 

 bundles, became more apparent, as also did the 

 significance of the ascending transpiration current ; 



