SPOROGONIUM OF MNIUM. 349 



The sporogonium, the so-called " moss-fruit," the study of 

 which we will carry on upon the same Mnium hornum, consists 

 of stalk or seta, and capsule. The base of the seta is sunk in 

 the tissue of the mother-plant. The result of fertilisation is here, 

 therefore, somewhat different to that in the Liverworts, and needs 

 a few words of explanation, further illustrated by Fig. 127. 

 After fertilisation, the oospore develops into an embryo, an early 

 stage of which is shown in Fig. 127, A. This embryo develops 

 in length both upwards and downwards ; downwards it grows 

 into a foot which, as the base of the seta, passes through the 

 tissue of the foot or stalk of the archegonium, and plunges into 

 that of the apex of the moss-stem. (See Fig. 127, B and C). 

 Upwardly, the embryo develops into the capsule, to be hereafter 

 described. The seta remains for a long time short. Accompany- 

 ing the increase in length, and likewise in thickness, of the young 

 sporogonium, the body of the archegonium, which had enclosed 

 the oosphere, also undergoes further development, keeping pace 

 with the sporogonium in its growth, so as continuously to cover 

 it. The upper part of the neck shrivels, as shown in Fig. 127, 

 B and 0, at the top. When, later in the development of the 

 sporogonium, the seta rapidly elongates, the body of the arche- 

 gonium, etc., is ruptured round its base, and is carried upwards, 

 covering the capsule as with a cap, the calyptra. This calyptra, 

 proceeding from the enlarged archegonium, which covers the 

 growing capsule, is in Mnium early cast off, so that it is usually 

 difficult to find. It is split up one side to its tapering apex, and 

 is composed of one, in part also two, layers of elongated cells. 

 The narrowed apex ends in a brown point, which indicates the 

 remains of the neck of the archegonium. At. the base, where it 

 was ruptured by the growing sporogone, it appears as if cut off. 

 The apex of the capsule, denuded of its calyptra, has a cover 

 or lid (operculum) provided with a short beak. With a needle 

 it can be easily loosed, when the edge of the capsular urn, fringed 

 with its teeth, comes to- view. The teeth form the peristome. 

 The upper part of the seta, passing into the capsule, is called the 

 apophysis. In the present case this last is separated from the 

 capsule by a very slight constriction, and is distinguished from 

 it by its brown colour. In some mosses, the apophysis is far 

 wider than the capsule. 



The Peristome. In order 'to study the structure of the peri- 

 stome, we take a cross-section through the capsule, close under 



