340 Mosses. 



points of structure, the Moss tribe is of a mest singular nature 

 Mosses are said to be in fruit, when the stems are furnished 

 with brown hollow cases, seated on a long stalk. It is chiefly 

 of this fruit, or theca, or sporangium, and its modifications 

 that we make use in distinguishing the genera. Let it there- 

 fore engage our attention first. No species can be more com- 

 mon than Wall Tortula (Tortula muralis), dark tufts of which 

 are found everywhere, upon the north side of walls, growing 

 out of the mortar. The theca of this plant wears a little cap 

 not unlike that of the Norman peasant women, with its hi<*h 

 peak, and long lappets : this part is called a calyptra : when 

 young, it was rolled round the theca, so as completely to cover 

 it over, like an extinguisher; but when the stalk of the theca 

 lengthened, the calyptra was torn away from its support, and 

 carried up upon the tip. After a certain time, the calyptra 

 drops off; and at that time the theca is in the best state for ex- 

 amination. You will find it terminated by a conical lid, or 

 operculum, which is thrown off when the spores, or reproduc- 

 tive parts, are fit to be dispersed. When the lid has been thus 

 spontaneously thrown off, a new and peculiar set of parts 

 come in view — you will find that the lid covered a kind of 

 tuft of twisted hairs, which at first look as if they stopped up 

 the mouth of the theca. But if you cut a theca perpendicu- 

 larly from the bottom to the top, you will learn from the sectional 

 view that you will obtain of the parts, that, in reality, the 

 hairs arise from within the rim of the theca, in a single row. 

 These hairs are named, in Botany, the teeth of the fringe, or 

 peristome,' the latter term designating the ring of hairs. The 

 nature of the fringe varies in different genera; sometimes it 

 consists of two rows of teeth, differing from each other in size 

 or number, or arrangement : some have only four teeth, others 

 eight, or sixteen, or thirty-two, or sixty-four ; in all cases, their 

 number is some multiple of four; a curious circumstance, which 

 shows the great simplicity of design that is observed in the 

 construction of these minute objects. The fringe is not, how- 

 ever, always present : there is a small section of the Moss 

 Tribe, all the genera of which are destitute of this singular or- 

 gan. What office it may have to perform, we can only guess. 

 It seems to be connected with the dispersion of the spores ; and 



