VEGETABLE ORGANIZATION. 



70 



with in those parts exclusively which are above 

 the water. The leaves of the Ranunculus 

 aquaticus, 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 circumstances, and in particular exi- 

 gences. 



The principal organs through which the 

 fluids that serve for nourishment are received 

 into the system of plants, are those situated at 

 the extremities of the roots, where they are 

 termed, from their peculiar texture, spongioles* 



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

 spongiole ; the arrangement of the cells composing which is 

 shewn in Fig. 24, from De Candolle. 



