Chap, ii.] VEGETAL NUTRITION. 89 



plant, either simultaneously in the state of water, or isolatedly. 

 It is probable, in efiect, that the green parts of plants have the 

 power of decomposing water, which they draw in a small part 

 from the atmosphere, but in enormous quantity from the soil. 

 The chlorophyllian parts would effect the decomposition of water, 

 whatsoever its source, and would fix direct its elements in the 

 complex combinations of which we have spoken. This, however, 

 is a point which has not yet been well studied. Certain, at least, 

 it is, that the greater part of the oxygen absorbed by the plant 

 is taken from the atmosphere direct, and a little by all parts of 

 the vegetal organism. As to carbon, which forms in weight the 

 chief part of every desiccated plant, it also is derived by the 

 green poi-tions of the plants from the carbonic acid of the air. 

 This is one of the most interesting, one of the best studied points 

 of vegetal physiology. All the other mineral matters, and 

 almost the whole of the water, are absorbed by the roots of the 

 plant, penetrate into the vegetal tissues, there ascend, there meet 

 with, especially in the leaves, the mineral substances derived from 

 the air, and some of them form complex combinations. 



Vegetal physiology is still so confused, the division of labour 

 in the plant is so ill-distinguished, that it is not easy to mark out 

 therein functions thoroughly determinate, functions very dif- 

 ferent from each other. Everything is connected, everything 

 blends, everything forms the link of a chain. Nevertheless, for 

 clearness of exposition, we are obliged to make divisions more or 

 less natui'al ; we must, in effect, speak of phenomena mingled, 

 entangled, proceeding sometimes simultaneously in the same 

 tissues or organs. We have to tell how penetrate into the 

 plant the numerous mineral substances which chemical analysis 

 discovers there, how those substances have infiltrated themselves 

 into the tissues, what compounds they have formed there under 

 the powerful action of the nutritive movement, finally how and 

 in what proportion they were eliminated during the life of the 

 plant after becoming unsuitable to figure in the nutritive 

 process. 



