THE PROCESS OF VEGETATION. 11 



not algee and confervse, but gigantic plants growing on dry land — 

 land hard and dry as the mountain brow. And to another phase of 

 vegetation promoted by the absorption of moisture attention may 

 now be given. 



As with algse so with grasses and herbs, and shrubs and trees, their 

 whole structure is built up of cells, some of which may have been 

 elongated into vessels, or otherwise metamorphosed; and the dry 

 dead cell walls of these constitute the pith and the woody fibre of 

 which trees seem chiefly composed. Of some of the vessels through 

 which the milk sap flows it may be that they have been formed 

 otherwise ; but the principal difference between the gigantic tree 

 and the gigantic sea-weed in the source of growth is only this, that 

 while the latter absorbs nutriment over the whole of its surface the 

 former does it mainly by the roots, and almost exclusively by the 

 cells at the extremities of the rootlets, where are masses of them, 

 which have, in reference to this function, received the designation 

 spongioles, or little sponges, resembhng these as they do, not in their 

 structure, indeed, but in their power of absorption. They are often 

 represented in cuts as rounded elongated expansions, but they are 

 not always to be so seen by the enquiring learner; examined micro- 

 scopically, they appear as numerous unprotected living cells at the 

 extremities of the rootlets, of which those furthest from the root to 

 which they belong continue to increase and multiply with rapidity in 

 appropriate soil, while those behind, and nearer to the stem, seem to 

 have lost in a great measure this power of reproduction. 



It may seem that the absorbing surface bears but a very small pro- 

 portion to the entire bulk of the plant, and I am not concerned to 

 dispute the correctness of the conclusion that proportionally it is 

 small, but what is proportionally small may be absolutely great. 

 Count the rootlets of an onion, or of a leek, or of a stalk of wheat, 

 and estimate if you cannot measure the superficial extent of the 

 spongioles ; calculate if you cannot count, and estimate if you cannot 

 even calculate, the hair-like fibrillaj of the roots and ramified rootlets 

 of a shrub or a tree, and by reasoning try to form some idea of the 

 vastness of the superficies of the spongioles there, and you may find 

 that it is not to be despised. Bear in mind that much of the mass of 

 a growing tree is fixed and stable, — that a small streamlet may have 

 filled and may keep filled an extensive lake, provided only the out- 

 flow do not exceed the supply, — that a very small orifice or mouth, 

 and that used only occasionally for the purpose, may suffice and does 

 suffice for the feeding of a man or other animal, — and any prejudice 



