HOW PLANTS DRINK. 57 



manufactured. These useful 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 vege- 

 table, protoplasm, we must have a fourth element, 

 nitrogen ; and that element is supplied by the roots 

 in 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, ni- 

 trogen, 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 im- 

 portant of these are sulphur and phosphorus. 

 The plant, however, does not take in these sub- 

 stances in their free or simple form, as nitrogen, 

 sulphur, and phosphorus, but in composition, 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 which 

 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 ex- 

 tremely complex body, called protoplasm; and 

 this protoplasm is the ultimate living matter, the 

 " physical basis of life ; " the thing without which 

 there could be no plants or animals possible. 



What is protoplasm this mysterious stuff, 

 which builds up the bodies of plants and animals ? 

 It is a curious transparent jelly-like substance, 

 full of tiny microscopic grains, and composed of 



