148 VEGETABLE CELLS. 



nutriment. But just the reverse occurs here, and it is 

 actually the lateral face which expands. The assumption 

 that the lateral face is at all enlarged by portions of the 

 end face being pushed over to the side is impossible here, 

 since this must necessarily remove the branch-cell gra- 

 dually away from the end. That the branch-cell is not 

 all moveable on the lateral face, and that its situation 

 may be regarded as a safe criterion here, is proved by the 

 pore which the branch-cells of the Callithamniaceoe pos- 

 sess in the centre of their basal surface, and which cer- 

 tainly is not moveable.. The same may be observed in 

 Ceramiaceae and in other Floridese ; as, for instance, in 

 Polysiphonia, where the prismatic central cell frequently 

 bears a branch. 



The objection that the plants mentioned live in water, 

 does not appear to me an important objection. For it 

 can certainly at most be asserted, that membranes in 

 contact with water will be more readily nourished than 

 those exposed to the air ; but not that membranes which 

 are moistened with water, possess a more active nutrition 

 than such as are applied against other cells. Besides 

 which, that objection will, in any case, not apply to Poly- 

 siphonia, where the elongated central cells, the growth 

 of which furnishes the same result, are wholly surrounded 

 by cells. In order further to settle that doubt, I may 

 add that cylindrical cells, the lateral faces of which are 

 exposed to the air and the ends applied to cells, also, as 

 for instance in several filamentous Fungi and many hairs 

 of Phanerogainia, exhibit a similar condition to that of 

 the cells forming the joints of the Callithamniacese ; that, 

 namely, their lateral faces expand considerably more than 

 their end faces, which here alone officiate in the recep- 

 tion and transmission of fluid nutriment. The growth 

 of the cell may be judged of here again by the relative 

 position of the branch-cell, and in addition by the rela- 

 tive position of the nucleus of the cell. Hairs consisting 

 of a single cell, are originally little hemispherical or 

 conical cells ; the parietal nucleus lies at some point of 



