INTRODUCTION. XV 



believe, that the direction is sufficiently constant in any species to 

 afford a good character of distinction, and it is only in a very few 

 cases that I have relied upon it. 



When the calyptra falls off or is removed the capsule is 

 exposed ; it is usually more or less elliptical, but is frequently 

 elongated and cylindric, equally often shortened and even globose, 

 or it maybe pyriform ; it is often striated (Tab. IV. n, 18), more 

 rarely angular (Tab. IV. 14) ; it is erect (Tab. IV. 9), inclined 

 (Tab. IV. 12), cernuous (Tab. IV. 14), or even pendulous (Tab. 

 IV. 13), and it is often more or less curved, or asymmetric. There 

 are other forms which it less commonly assumes. 



The capsule may be cleistocarpous, that is without any 

 regular orifice or lid, but bursting irregularly; rarely it opens by 

 valves (Tab. IV. 7). Usually, however, it opens with a lid, 

 resembling the lid of an urn ; this falls off at maturity, its rupture 

 being often assisted by the unrolling of the annulus, a very highly 

 elastic ring of cells surrounding the orifice at the point of juncture 

 with the lid, and rolling back with considerable force and rapidity 

 when the capsule is fully ripe. The annulus is however not 

 always present. 



The spores are usually produced in great numbers, and 

 are green or brown ; they are either smooth, or papillose or 

 tuberculate ; almost always more or less globose, rarely angular. 

 They range, in point of size, with a few exceptions, between 10 

 and 25 /1 in diameter. They usually surround a central column of 

 tissue, called the columella, which is sometimes long enough to be 

 distinctly visible above the mouth of the capsule after the fall of 

 the lid, and occasionally is united to the interior of the lid, 

 retarding its fall for a time and finally falling off with it. 



The mouth of the orifice after the removal of the lid is in 

 some mosses a bare rim, when the capsule is termed gymnostomous ; 

 but more frequently it is furnished with a fringe surrounding and 

 in part closing the mouth; this fringe is termed the peristome, 

 and affords, owing to the numerous forms and degrees of 

 development it assumes, and its constancy throughout large groups 

 of mosses, a very important basis of classification, especially as 

 regards Orders and Genera. The researches of Philibert and 

 others have recently brought into clearer light the great importance 

 of this organ from a systematic point of view ; and as the main 

 ■divisions in the present work are based upon its structure, the 

 student will do well to become familiarised with its general 

 character and the terminology employed in its description. 



