50 THE PLANT. 



that the want or excess of the mineral substances indis- 

 pensable for the production of those matters must exercise 

 a very decided influence upon the growth of the plant, 

 and upon the formation of the leaves, roots, and seed. 

 Want of azotised and excess of fixed nutritive substances 

 would lead to the formation of unazotised materials in 

 preponderating quantity ; but when these have assumed 

 the form of leaves and roots, they retain a certain amount 

 of nitrogenous matter, thereby impairing the seed forma- 

 tion, a principal condition of which is an excess of proto- 

 plasm. An excess of azotised food, with a deficiency of 

 fixed nutritive substances, will be of no use to the plant 

 itself, because the latter can for its organic operations 

 make use of nitrogenous substances only in proportion as 

 they exist in the protoplasm, and the contents of the 

 cell are of no value to the plant in the absence of the 

 materials required to form the cell-walls. 



In the process of animal hfe the organs of the body are 

 constructed from the elements of the egg ; the constituent 

 parts of such constructed organs are azotised, whereas in 

 the plant they contain no nitrogen. All processes of 

 vegetative life tend simply to produce the elements of 

 the seed. The plant only lives in generating the egg- 

 constituents and the egg itself ; the animal only fives by 

 destroying these very egg-constituents. 



On one and the same soil equally suited for the turnip 

 and the wheat-plant, the former produces for the same 

 amount of azotised substance twice as much unazotised 

 matter as the latter. It is manifest that if two plants 

 produce vsdthin the same time different quantities of 

 hydrates of carbon (wood, sugar, and amylum), the 

 organs of decomposition must be arranged in a manner 

 not only to afford adequate room for the carbonic acid 

 supplying the carbon, and for the water supplying the 



