50 THE TISSUES OF PLANTS 



exists in the primordial utricle or mucilaginous lining of 

 all young and growing cells. The permanent wall of the 

 cell is formed under its influence, and it is one of the ele- 

 ments of vegetable albumen, fibrin, caseine, and glutine, 

 but it makes no part of the permanent frame-work of plants. 

 Nitrogen, on the other hand, enters largely into the com- 

 position of the animal tissues, which are generally quater- 

 nary compounds, consisting of carbon, oxygen, hydrogen, 

 and nitrogen. 



