18 NATURE OF SPONGELETS. 



any fluid or gaseous matter that may be presented to them. 

 On this account they are usually caUed spongelets. 



In the roots of ordinary exogens, when the tissue is very 

 young, the spongelet (Fig. I. a) consists of very lax tender 



Fig. I. — Section of a Spongelet, magnified. 



cellular tissue, resting upon a blunt cone of woody matter, 

 composed principally of woody tubes, and connected with the 

 alburnum of the stem (Fig. I. h) ; it is, therefore, placed in the 

 most favourable position possible for communicating to the 

 general system of circulation the fluids taken up by its highly 

 absorbent tissue. In some roots a cap exists, called a 

 •pileqrhw, which guards as it were the spongelet beneath it, 

 or forms part of the spongelet. 



It is the opinion of most vegetable physiologists, that the 

 absorbing or feeding powers of roots are conducted principally 

 at these points; and that the general surface of the root 

 possesses little or no power of the kind. And, indeed, it seems 

 highly probable that this is so, when we consider how thick is 

 the bark of the root, through which fluids would have to pass 

 before they reach the alburnum- 



But although there can be no doubt that the spongelets act 

 as absorbents with more force than any other part of the root, 

 yet it is equally certain that the whole surface of young roots 

 also possesses an absorbing, property, only in a more limited 

 degree. It is not until their tissue is solidified that roots 



