PHYSIOLOGY. 69 



separation of the phenomena of the living body from all 

 those which are comprised in the sciences of chemistry 

 and mechanics on the one hand, and of pure metaphy- 

 sics on the other ; and the general acknowledgment 

 of referring all the facts which the human body pre- 

 sents in health and disease, to laws of vitality, exem- 

 plified in the history of other living bodies, but not in 

 other departments of nature." (Alison of Edinburgh.) 

 It is not the design of this work to enter into a consi- 

 deration of the general conditions of vital action, or of 

 the vital powers or forces by which these vital actions 

 are maintained, but to proceed at once to a notice 

 of those different functions and processes of the body 

 which are always a more or less complicated series of 

 them. 



2. Before speaking of the various functional pro- 

 cesses in detail observed to take place in a living plant, 

 we may notice here shortly the office of the elementary 

 forms of structure. 



3. Cellular tissue is capable of transmitting fluid and 

 secreting properly elaborated material where no other 

 tissue exists ; it acts as a reservoir for nourishment for 

 the plant at certain periods, and as a receptacle for its 

 secreted products and juices ; it binds and connects the 

 various compound organs of a plant firmly together, and 

 must be looked upon as analogous to the cellular pa- 

 renchyma of animal structures. 



4. Fibre supports and strengthens the plant by its 

 firmness and tenacity, and is capable of transmitting 

 the fluids both upwards and downwards, and is some- 

 times a receptacle of colouring and secreted matters. 



5. Vascular tissue, consisting of spiral vessels and 

 ducts, present, in regard to the functions of the former, 

 some difficulty ; many physiologists consider their func- 

 tion to be that of merely conveying air at all times, 

 whilst others have argued for their transmission of 

 fluids : to me the argument seems to be in favour of the 

 supposition that the spiral vessels do at certain periods 

 of the plant's life convey fluid, though they may at 



