50 THE TISSUES OF PLANTS 



exists in the primordial utricle or mucilaginous lining of 

 all- young and growing cells. Tlie permanent wall of the 

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

 ments of vegetable alhumen, 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. 



