THE HIGHER CRYPTOGAM I A. 195 



the contents of these cells, proceed from above downwards ; 

 the process taking place rapidly at first, and afterwards 

 more slowly. 



After the formation of the canal of the neck, and whilst 

 the apex of the archegoninm is still closed, the walls of the 

 cells of the peripheral layer become arched inwards to a 

 considerable extent, and protrude into the canal : a mani- 

 fest proof that these cells, being in a state of active expan- 

 sion, exert a great pressure upon, and displace the fluid 

 contents of the canal. Ultimately the cells of the apex 

 part asunder, by which means a portion of the mucilaginous 

 fluid contained in the canal usually escapes through the 

 opening. By this means individual cells are not unfre- 

 quently detached and thrust off 1 (PI. XXV, fig. 12). The 

 canal is now open externally, and exhibits an uninterrupted 

 communication from without inwards, up to the central 

 cell of the archegonium. 



The membrane of the arch of the apex of the latter has 

 in the mean time become softened. A gentle pressure upon 

 the covering glass not only forces the mucilage of the canal 

 out of the mouth of the latter, but a portion also of the 

 contents of the embryo-sac is gradually driven into, and 

 through the canal. The motion however is not so sudden 

 as in the case where the contents of a cell escape through a 

 fissure produced by the bursting under pressure of an elas- 

 tic membrane. In one case I observed that one of the 

 bodies in the canal had made its way into the central cell ; 

 a circumstance which proves clearly the exposed nature of 

 the embryo-sac (PI. XXV, fig. II). The membrane of the 

 germinal vesicle on the other hand, even before the burst- 

 ing of the archegonium, is somewhat firmer. It is clearly 

 seen, when an embryo-sac and the germinal vesicle within 

 it are injured in making a section, that the membrane 

 exhibits folds (PL XXV, fig. 9). 



Most archegonia are not developed any further. The 

 cell-walls which adjoin the canal, as well as the large cell 

 at the base of the archegonium, assume the purplish-brown 

 colour, which is peculiar to the fading cell-membranes of 

 almost all the higher cryptogams. This is the fate not 



