CH. YIII.] THE DISEASES OF PLANTS. 249 



we shall find the close analogy still continues, for 

 they contain in common, sugar, mucus, jelly, colour- 

 ing matters, gluten a, fibrin, oils, resins, and ex- 

 tractives. 



The fimctions of animals and plants ai'e in a like 

 degree analogous. Animals take in their food by the 

 agency of the mouth, and prepare it for -digestion 

 either by various degrees of mastication, or by attri- 

 tion, as in the gizzards of birds. In this they differ 

 from plants ; but these have a sufficient compensa- 

 tion, inasmuch as that they imbibe their food in a 

 fluid foi-m, liquid or aeriform, and consequently in a 

 state already of the finest possible dirision. Animal 

 and vegetable remains ai'e their common food, and 

 salts of various kinds are their condiments and stimu- 

 lants ; plants having this advantage over animals, 

 that as they absorb only the soluble and finer parts 

 of their nutriments, and their absorbing organs have 

 the power of rejecting that which is offensive, they 

 have no offensive matters to sepai'ate such as appear 

 in the excrements of animals. 



In the animal stomach the food undergoes an ex 

 tensive change, being reduced to a pulp of greater 

 specific gravity, and being altered entirely both in 

 taste and odoui'. In the sap vessels of plants, which 

 may be tinily considered as their primary organ of 

 digestion, their food or sap undergoes a change pre 

 * The gluten of plants is the albumen of animals. 



