^1] 



UPON THE RATE OF GROWTH 



307 



matter, e.g. insects, as food. Fungi and animals obtain their 

 carbon from carbon compounds elaborated by plants. The 

 indispensableness of carbon for the life of all organisms as well 

 as for their growth requires no illustration. 



Nitrogen. — Of the importance of nitrogen as a hylogenic 

 food nothing more need be said than that it is essential to the 

 formation of albumen. The ordinary form in which nitrogen is 





a If 



A 



V > I ' 



*" f! 



J)'. 



f 



Pig. 85. — Cultures of Sinapis alba in pure quartz sand, to ■wliich have been added 

 equal amounts of a nutritive solution, but unequal quantities of nitrogen in the 

 form of calcic nitrate, as follows : A, without nitrogen : B, 0.1 gramme calcic 

 nitrate in each vessel ; C, 0.6 gramme calcic nitrate in each vessel. After a photo- 

 graph. From Frank ('92). 



obtained by the seedling is, as already stated (p. 298), that of 

 the nitrates or ammonia in the soil (Fig. 85). Growing fungi 

 gain it chiefly from nitrogenous organic compounds, but many 

 fungi can make use of ammonium nitrate for this purpose. 

 Growing animals gain nitrogen chiefly, if not exclusively, from 

 organic compounds, especially albumen and allied substances. 



Free nitrogen is found wide-spread in nature. It forms 

 about 79% of the volume of the air ; penetrates into water, 

 though in a smaller proportion than in the air, and even into 

 the soil. Thus for organisms living in any of these media free 



