ANTHERIDIUM OF MNIUM. 345 



can see that dehiscence takes place at the apex by means of a 

 number of recurved teeth. The elaters are strongly hygroscopic, 

 bend to and fro with hygroscopic changes in the atmosphere, and 

 so assist the dissemination of the spores. 



The sexual organs are not raised upon special receptacles in 

 all the Marchantiacese, and in other Liverworts this structure 

 is altogether wanting. On the other hand, the stalk of the sporo- 

 gonium in many cases elongates considerably, and carries up the 

 oapsule with the spores, thus assisting the dissemination of the 

 spores. 



Antheridia of Mnium. The antheridia of the leaf-bearing 

 Mosses are best examined in a genus which has striking male 

 "flowers". We choose a representative of the genus Mnium, 

 e.g., the widely distributed Mnium hornum, which in May and 

 June "flowers" very freely, and bears female flowers and sporo- 

 gonia at the same time. The male flowers are, it is true, much 

 more striking than the female, and it is often necessary to search 

 longer for these latter. The male flowers are dark-green, disk- 

 shaped, surrounded by a rosette of leaves, the involucre or peri- 

 chaetium, Towards the interior of the flower these leaves 

 decrease rapidly in size. In the axils of the outer, but chiefly, 

 however, of the inner, perichaetial leaves, stand numerous anthe- 

 ridia and paraphyses, which also spread over the entire apex of 

 the axis. This is easily shown by median longitudinal sections of 

 the flower, which are best prepared between the fingers, turning 

 the apex downwards in cutting. On these longitudinal sections 

 we see that the flower-axis broadens, after the fashion of a floral 

 receptacle, at the place of insertion of the sexual organs, and in 

 the middle is even a little hollowed. The central conducting 

 bundle, peculiar to species of Mnium (see p. 228), has undergone 

 a corresponding broadening, and ends in a chlorophyll-containing 

 tissue, which spreads out under the receptacle. The antheridia 

 and the paraphyses are at once recognised as such, and their 

 structure is easy to understand (see Fig. 125 A). The antheridia 

 are club-shaped, shortly-stalked bodies, somewhat tapering at 

 both ends. The cells of their wall contain numerous chlorophyll 

 grains. Where the longitudinal section has opened an anthe- 

 ridium, we see that its wall is composed of a single layer 

 of cells. The contents of the antheridium consist of small, 

 colourless cells, the partition walls of which in young stages of 

 development clearly show rectangular arrangement. The ex- 



