COMPAEED WITH THOSE OP ANIMALS. 45 



every thing else, tlie fat cells select the fatty matters, mus- 

 cle produces muscle, bone generates bone, nerve developes 

 nerve, all drawing the appropriate materials from the same 

 fluid; just as some of the cells of plants select from the sap 

 starch, others oils, others fluid coloring matters ; or as the 

 gelatinous tissue called cambium, interjacent between the 

 bark and wood, generates during the season of vegetable 

 growth, beds of the same nature as those with which it is 

 in immediate contact, and is developed into ligneous and 

 cortical fibre, wood producing wood, bark forming bark, 

 the tissues preserving their cellular organization only in 

 those portions which correspond to the medullary rays. 

 Here again we see the operation of the same laws in animal 

 and vegetable matter. 



We know nothing as to the modus operandi of the pro- 

 cesses in the cell-laboratory, by which these various 

 organic products are formed. It is evident that they are 

 physiologically connected with the growth of the other parts 

 of the organism ; for the vitality of all the organs of plants 

 is exhausted in succession, in developing the germ. To 

 this tend all those vital changes which take place in the 

 cells and organs of plants and animals, throughout all the 

 ever varying phases of their existence. Here, again, we 

 are in the dark as to the physiological uses to which many 

 of the various products of the cells are appropriated, in the 

 animal and vegetable economy. Many of the organic pro- 

 ducts of plants are so valuable as food and medicine to the 

 animal creation and to man, that their preparation would 

 appear to be the leading function of the plant, and the grand 

 reason of its development. 



The individuahty of the cells of organized beings, is fur- 

 ther proved by their different periods of life. Many of 

 them are developed only to serve a temporary purpose, — 



