i64 . MOSSES AND FERNS ' chap. 



may be plentiful, they fail to be fecundated and thus no cap- 

 sules are developed. This no doubt accounts for the extreme 

 rarity of the sporogonium in many Mosses, although in other 

 cases, e. g., Sphagnum^ it would appear that the formation of 

 the sexual organs is a rare occurrence. These resemble in gen- 

 eral those of the Hepaticse, but differ in some of their details. 

 The leaves surrounding them are often somewhat modified, 

 and in the case of the male plants (Atrichmn, Polytrichum) 

 different in form and colour from the other leaves, so that the 

 whole structure looks strikingly like a flower. As a rule, the 

 archegonial receptacles are not so conspicuous. The early 

 divisions of the archegonium correspond closely with those of 

 the Liverworts, but after the "cover cell" is formed, instead 

 of dividing by cross walls into four cells, it functions for some 

 time as an apical cell, and to its activity is largely due the fur- 

 ther development of the neck. The venter is usually very 

 much more massive than in the Hepaticse, and the egg small. 



The antheridia, except in Sphagnum, are borne also at the 

 apex of the stem, whose apical cell does not always, at any rate, 

 become transformed into an antheridium, as we sometimes find, 

 especially in species of Atrichum and Polytrichum, that the 

 axis grows through the antheridial group and develops a leafy 

 axis, which later may form other antheridia at its apex. Where 

 the plants are dioecious the males are usually noticeably smaller 

 than the females. The antheridia, except in Sphagnum, are 

 very uniform in structure, and like the archegonium exhibit a 

 very definite apical growth (Fig. 102). The wall remains 

 one-layered, as in the Liverworts, and often the chromatophores 

 in its cells become red at maturity, as in some Liverworts, e. g., 

 Anthoceros. The ripe antheridium is in most Mosses club- 

 shaped, and the sperm cells are discharged while still in con- 

 nection, the complete isolation of the sperm cells only taking 

 place some time after the mass has lain in water. In Sphag- 

 num the antheridia are much like those of certain leafy Liver- 

 worts, and stand singly in the axils of the leaves of the male 

 branches. 



Holferty (i) describes and figures a number of Interesting 

 abnormalities in Mniuni cuspidatiim in which organs are some- 

 times developed which are intermediate in character between 

 archegonia and antheridia. 



The sporophyte of the Mosses reaches a high degree of 



p 



