ON THE DEVELOPMENT AND STRUCTURE OF MOSSES. 23 



The walls of the spore-sac are generally even, but in Poly- 

 trichum and some neighbouring genera they are strongly 

 puckered. The spore-sac is at first filled with a nearly uni- 

 form cellular mass. The component cells are at length diffe- 

 rentiated, some remaining abortive, and others, by crucial cell- 

 division, producing the spores within the cavity. In a few 

 cases spores have been generated within the tissue of the colu- 

 mella, but this is quite exceptional. In general they separate 

 from each other, when mature retaining occasionally, as in 

 Archidium, something of the angular form, produced by mu- 

 tual pressure (Crypt. Bot. fig. 102), but sometimes they are 

 perfectly globose. In an exotic Moss, Eucamptodon perichae- 

 tialis, the cell-division is continued further, and the eight re- 

 sultant spores are permanently retained in the mother-cell, so 

 far as observations have hitherto been carried (Crypt. Bot. fig. 

 99 c). In Splachnum they radiate regularly from the columella. 



When the columella has performed its functions, which con- 

 sist probably in supplying nutriment to the spore-sac, it dries 

 up, and sometimes remains attached to the tissue at the apex, 

 with which it is either continuous, or, as in Polytrichurn and 

 Sphagnum, perfectly distinct. In Polytrichurn it forms a di- 

 lated membrane, closing up the spore-sac above and prevent- 

 ing the too hasty dispersion of the spores. 



The top of the sporangium or lid, except in a very few genera, 

 where it remains permanently attached, and the spores escape 

 only by the decay or irregular rupture of the walls, separates 

 from the rest, just in a line with the top of the spore-sac, by a 

 regular horizontal fissure, the fissure being either quite uniform 

 or furnished with a rigid or elastic ring, consisting of a varia- 

 ble number of cells, sometimes only a single row, which either 

 separate immediately on the bursting of the lid, or remain 

 permanently attached. One of the best examples is afforded 



