M. Mohl on the Growth of Cell- Membrane. 149 



the cells of the endothccium of anthers, the inner layer forms a 

 continuous layer on one side of the cell, while on the other it is 

 split into fibres which run out like rays from the membranous 

 portion, — a distinct proof that fibres and membrane are merely 

 different varieties of form of one and the same element of the cell. 

 Lastly, it may happen that the inner membrane is only deposited 

 along the angles of the cells, and not on the surface, and forms 

 semicircular borders projecting more or less into the cavity of 

 the cell. 



If now it be proved, and I believe that I have furnished the 

 proof in the foregoing, that the membrane of young cells pos- 

 sesses no openings, and if by following the development of cells 

 we see in an indubitable manner that their membrane becomes 

 gradually thicker, and that in these thickened cells, under all 

 circumstances*, an imperforate membrane is present on the ex- 

 terior, while in the layers lying on the inner side of this mem- 

 brane, and becoming continually thicker, there are holes which 

 in proportion as these layers become thicker assume the form of 

 canals, which are closed externally and open to the cell-cavity ; 

 when we further see that this inner membrane is not homoge- 

 neous, but consists of many, superposed, delicate lamellae, — in 

 these mechanical relations, in the earlier presence of an imperfo- 

 rate membrane and in the subsequent production of the inner, 

 continually thickening mass perforated with holes, lies a necessity 

 for the assumption that this latter layer is of later origin, and 

 has been deposited upon the inner side of the imperforate mem- 

 brane. In these relations there is throughout no ground for the 

 further assumption that the lamellse, which constitute the inner 

 secondary layer, have also become deposited in a series from 

 without inwards ; but mechanical relations occur in peculiar 

 cases which would make any other assumption appear very im- 

 probable. In evidence of this we have the fact, that in very thick- 

 walled cells many of the canals of the dots converging toward 

 the interior of the cell become blended ; especially however that 

 in cells which merely deposit a secondary layer in the angles, 

 these possess a form convex toward the cavity of the cell, and 

 consist of many superposed layers convex to the interior ; and that 

 in these cases we find in the young cells only few and narrow layers 

 of this kind, while in the full-grown cells a number of broader 

 layers lie upon the inner side of this narrow onef. 



These are briefly the anatomical grounds which decided me in 



* Those rare cases in which an absorption of the free membrane in the 

 canals of the dots takes place subsequently, from only an apparent excep- 

 tion. 



t Vide Bot. Zeit. ii. 323. tab. 2. figs. 2, 3. Scientific Memoirs, vol. iv. 

 p. 106. plate 1. figs. 2, 3. 



