VEGETABLE orftANIZATION. 



69 



leaves of the Ranunculus aquaticus, when made to grow 

 in the air, acquire stomata, but lose them entirely when grow- 

 ing under water. Stomata are wanting in all plants whose 

 structure is wholly cellular. 



Botanists are far from being agreed as to the precise func- 

 tions which the stomata perform. Their usual office un- 

 doubtedly is to exhale water; but they probably also absorb 

 air under certain circumstances, 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 extremities of the roots, where they are 

 termed, from their peculiar texture, spongioles.^ Of the 

 functions of spongioles in absorbing fluids I shall have occa- 

 sion to speak when treating of nutrition. But as the roots 

 exercise a mechanical as well as a nutrient office, we should 

 here consider them in the light of organs adapted to procure 

 to the plant a permanent attachment to the soil, upon which 

 it is wholly dependent for its supply of nourishment. It is 

 scarcely necessary to point out how effectually they perform 

 this office. Our admiration cannot fail to be excited when 

 we contemplate the manner in which a large tree is chained 

 to the earth by its powerful and widely spreading roots. By 

 the firm hold which they take of the ground, they procure 



* Fig. 23 exhibits tlie termination of a root of a willow in a sponglole; 

 tlie arrangement of the cells composing which is shown in Fig. 24, from Dc 

 CandoUe. 



