CELLS, THE ESSENTIAL ORGANS OF LIFE. 23 



in the water till they become fixed to some other body, 

 and then reproduce cells, which are aggregated after 

 the same pattern as in the parent plant. The common 

 mould or mustiness is a cluster of plants formed of cells 

 only : and there are some vegetables in which the entire 

 plant consists of but one isolated cell; such are the yeast 

 fungus {Torula cerevisice), and the red snow (Leparia 

 nivalis). In these examples we have proof that all those 

 functions in which the organic life of vegetables essen- 

 tially consists, namely, absorption, assimilation, the fixa- 

 tion of carbon from the atmosphere, respiration, exhala- 

 tion, secretion, and reproduction, are effected by one 

 simple cell. Even in the highest and most complicated 

 orders of vegetables, in which there is a variety of or- 

 gans adapted for the performance of different offices, 

 these functions are performed by the agency of cells, 

 which obtain materials of formation and support from 

 the ordinary chemical agents around them. Thus, an 

 aggregation of simple cells forms the cellular tissue ; a 

 fusion or blending of several cells produces the vessels, and 

 so forth ; and by cells are elaborated the gum, resin, oil, 

 starch, gluten, &c. ; and, by cells specially endowed, are 

 secreted the narcotic of the poppy, the deadly poison of 

 the nightshade, and the stimulant aromatic of the clove. 

 In like manner, in animal structures, all the various pro- 

 cesses of vitality are performed by cells or globules. 



