lf)3 PHYSIOLOGY 0]F VEGETABLES. 



dium of vascular communication between the root and 

 these parts. 



3. The Leaves serve to effect important changes in 

 the juices of the plant, as is presently to he explained. 



4. The Fructification forms a distinct set of organs 

 for the continuation of plants in succession, one genera- 

 tion after another. For the particular physiology of 

 this part, ^^fructification, p. 45. 



II. Thz Circulation of the Blood in Jlnimals. 



Physiologists observe an analogy between animals 

 and vegetables, both in anatomical structure and physi- 

 ological functions, which r;)akes it necessary to explain, 

 especially, the circulation in animals, which is very 

 analogous to what we are about to explain in vegeta- 

 bles. 



The blood passes out of the left cavity of the heart* 

 in the main trunk of the arteries, vUiich, dividing and 

 branching like a tree, takes a pretty direct course to 

 all the various p?rts of the body, where its branches 

 finally become innumerable, pervading every particle 

 of the body, and so small as to elude observation. These 

 are called the extreme vessels of the body. They grad- 

 ually collect themselves again into another set of 

 vessels, called the veins, which finally unite into two 

 principal trunks that enter the cavity of the right side 

 of the heart together, and convey the blood thither. 



By ite contractions the heart sends it from the right 

 cavity to the lungs, through a vessel which passes up 

 to them, ramifying, like the artery which has been de- 

 scribed, until it pervades every particle of the lungs 

 with its minute vessels, which are called the extreme 

 bloodvessels of the lungs. These finally collect them- 

 selves into another set of vessels, which enter the left 

 cavity of the heart in four trunks, and return the blood 

 to be recirculated. The extreme blood vessels, in the 

 lungs meet with the extreme branches of the trachea or 



f The heart has two cavities, a right and left, 



