How t>LANTS DEINiJi 61 



starches, oils, sugars, and so forth, all of which 

 contain a little oxygen, but far less than the 

 amount contained in the carbonic acid and water 

 from which they are manufactured. These use- 

 ful materials, however, though possessing energy, 

 that is to say the power of producing light and 

 heat and motion, are not exactly live -stuffs ; 

 in order to make out of them the living green 

 matter of leaves, chlorophyll, or the living cell- 

 stuff of all bodies, animal or vegetable, proto- 

 plasm, we must have a fourth elemefity nitrogen ;: 

 and that element is supplied by the roots m 

 solution. 



So now you see the full importance of the 

 roots ; they add to the oils and starches manu- 

 factured in the leaves that mysterious body, 

 nitrogen, which is necessary in order to turn 

 these things into protoplasm and chlorophyll. 



A few other things besides nitrogen are also 

 needed by the plant from the soil ; the most 

 important of these are sulphur and phosphorus. 

 The plant, however, does not take in these 

 substances in their free or simple form, as 

 nitrogen, sulphur, and phosphorus, but in com- 

 position, as soluble nitrates, sulphates, and 

 phosphates. 



Now, I am not going to trouble you with a 

 long chemical account of how the plant combines 

 these various materials — a thing about w^hich 

 even chemists and botanists themselves know as 

 yet but very little. It will be enough to say 

 here that the plant builds them up at last into- 

 an extremely complex body, called jjrotoi^lasin ;. 



