THE ROOT. 



denser tissue than that behind it.* The point of every branch of 

 the root is capped in the same way. It follows that the so-called 

 spongioles or spongelets of the roots have no existence. Not only 

 are there no such special organs as are commonly spoken of, but 

 absorption evidently does not take place, to any considerable ex- 

 tent, through the older tissue of the point itself. 



120. As to absorption by roots, the inspection of the root of a 

 germinating plantlet, or of any growing rootlet, even under a low 

 magnifying power, shows that they must imbibe the moisture that 

 bathes them, by endosmosis (37), through the whole recently formed 

 surface, and especially by the hair-like prolongations of the exterior 

 layer of cells, or fibrils, as they may be termed, which are copiously 

 borne by all young roots (Fig. 108). Fig. 109, 110, show some 

 of these root-hairs, and the tissue that bears them, more magni- 

 fied. These capillary tubes, of 

 great tenuity and with extremely 

 delicate walls, immensely increase 

 the surface which the rootlet ex- 

 poses, and play a more important 

 part in absorption than is gener- 

 ally supposed ; for they appear 

 to have attracted little attention. 

 These fibrils perish when the 

 growing season is over, or when 

 the root gets a little older ; at the 

 same time, the external layer of 

 cells that bears them, at first un- 

 distinguishable from the parenchy- 

 ma beneath, except perhaps in the size of the cells, hardens and 

 thickens into a sort of epidermis, or firmer skin, so as to arrest or 

 greatly restrain the imbibition. This epidermis (69) of the root 

 consists of less compressed cells than in parts exposed to the light, 

 and is destitute of stomates or breathing-pores (70). 



121. The growth of the root and its branches keeps pace with the 

 development of the stem. As the latter shoots upward and expands 

 its leaves, from which water is copiously exhaled during vigorous 



* It is a similar tissue that exfoliates from the point of some aquatic (as in 

 Lemna, Fig. 96), and many aerial roots (as in Pandanus), in the form of a 

 loose cup or sheath. 



