120 THE NXJTRITIVE FUNCTIONS. 



Assimilation in animals is therefore as plant-like as the 

 rest of the nutritive processes. 



A great many plants, when their sap has been digested 

 in the leaves, reject at their exterior various matters which 

 are often condensed and solidified. Thus the leaves of the 

 sycamore are covered with a saccharine matter ; the stems 

 of pines and firs exude resins, and the fruits of the bay- 

 berry (Myrica cerifera,) are coated with a thick vegetable 

 wax. In these instances, the plant excretes these sub- 

 stances which are the products of nutrition, but which are 

 not necessary for the accomplishment of that function. 

 Their appearance is the result of their superabundance in 

 the subjacent tissues, the distension of which is relieved 

 by this exudation. 



