VII THE BR VINE ^ 201 



little in depth, while those above this point become very much 

 larger and project beyond them. This narrow zone of cells 

 marks the point where when ripe the operculum becomes 

 detached. The latter, up to the time the sporogonium is ripe, 

 is composed of a close tissue without any intercellular spaces. 

 The epidermal cells, seen from the surface, are seen to be 

 arranged in spiral rows running from the base to the apex. 

 Its central part is made up of large thin-walled parenchyma, 

 continuous with the tissue of the columella. The archesporium, 

 therefore, is not continuous over the top of the columella, as in 

 Sphagnum and AndrecEa, but is cylindrical. The archesporium 

 forms simply a single layer of small cells, and occupies a very 

 small part of the sporogonium, much less, relatively, than in 

 any of the forms hitherto described. Before the final division 

 of the spores it divides more or less completely into two layers. 

 The cells resulting from this last division are the spore mother 

 cells, which separate soon after their formation and lie free in the 

 space between the inner and outer spore-sacs, where each one 

 divides into four tetrahedral spores. 



In the operculum, as the capsule approaches maturity, the 

 differentiation of annulus and peristome takes place. The 

 former consists of about four rows of cells (Fig. 98) that occupy 

 the periphery of the broadest part of the operculum. These 

 cells are very much compressed vertically, but are deep and 

 have their walls thicker than their neighbours. Just below 

 them are about two rows of similar cells, but somewhat less 

 compressed and with very thin walls. These latter cells mark 

 where the separation takes place, the annulus forming the rim 

 of the loosened operculum. 



The peristome arises from the fifth layer of cells from the 

 outside of the operculum. If a median longitudinal section of 

 a nearly ripe capsule is examined, the row of cells belonging 

 to this layer (Fig. 99, per) is at once seen to have the outer 

 walls strongly thickened, and this thickening extends for a 

 short distance along the transverse walls. The inner walls 

 of the cells also show a slight increase in thickness, but much 

 less marked than the outer ones. A similar thickening of the 

 cell walls occurs also in about three rows of cells which run 

 from the outside of the capsule to the base of the peristome, 

 and form the rim of the " theca " or urn. 



The epidermis of the whole capsule has its outer walls 



