VEGETABLE ORGANIZATION. 



69 



of the leaves, or on that of the stem. This is the 

 case with such aquatic plants as are habitually 

 immersed in water. In those that are only par- 

 tially immersed, stomata are met with in those 

 parts exclusively which are above the water. The 

 leaves of the Ranunculus aquaticiis, when made to 

 grow in the air, acquire stomata, but lose them 

 entirely when growing under water. Stomata are 

 wanting in all plants whose structure is wholly 

 cellular. 



Botanists are far from being agreed as to the 

 precise functions which the stomata perform . Their 

 usual office undoubtedly is to exhale water; but 

 they probably also absorb air under certain circum- 

 stances, and in particular exigences. 



The principal organs through which the fluids 

 that serve for nourishment are received into the 

 system of plants, are those situated at the extremi- 

 ties of the roots, where they are termed, from their 

 peculiar texture, spojigioles* Of the functions of 



* Fig. 23 exhibits the termination of a root of a willow in a 

 spongiole ; the arrangement of the cells composing which is shown 

 in Fig. 24, from De Candolle. 



