10 GENERAL TEXTURE OF PLANTS. 



living bein^T. Animals secrete milk and fat from food 

 which has no resemblance to those substances ; so Ve- 

 getables secrete gum, sugar, and various resinous sub- 

 stances from the uniform juices of the earth, or perhaps 

 from mere water and air. The most different and dis- 

 cordant fluids, separated only by the finest fihn or 

 membrane, are, as we have already observed, kept 

 perfectly distinct, while life remains ; but no sooner 

 does the vital principle depart, than secretion, as well 

 as the due preservation of what has been secreted, are 

 both at an end, and the principle of dissolution reigns 

 absolute. 



Before we can examine the physiology of vege- 

 tables, it is necessary to acquire some idea of their 

 structure. 



Much light has been thrown upon the general texture 

 of Vegetables by the microscopic figures of Grew, 

 Malpighi and others, repeated by Dr. Thornton in his 

 Illustration of the Linnaean System, but more espe- 

 cially by the recent observations and highly magnified 

 dissections of M. Mirbel. See his Table of Vegetable 

 Anatomy in the work already mentioned. From pre- 

 ceding writers we had learned the general tubular or 

 vascular structure of the vegetable body, and the exist- 

 ence of some peculiar spirally-coated vessels in many 

 plants. On these slender foundations physiologists 

 have, at their pleasure, constructed various theories, 

 relative to the motion of the sap, respiration and other 

 functions, presumed to be analogous to those of ani- 



