28o ARCHEGONIA OF LIVERWORTS AND MOSSES 



recognised (Fig. 150, B, E). The sperm at ozoids show the same 

 general structure as do those of Liverworts, and are liberated 

 in much the same way during wet weather, the mass of mother- 

 sells often being ejected to some slight distance. 



The female organs, or archegonia, which are essentially similar 

 in the two groups, differ markedly from those of Thallophyta. 

 They are flask-shaped structures (Fig. 154, B), composed of a 

 lower swollen part, or venter (v.), and a long neck (n.), which, in 

 Mosses, is often twisted. The neck is a tube consisting of a 

 single layer of elongated cells surrounding a narrow canal. The 

 latter is occupied by a row of naked neck-canal cells which 

 ultimately become mucilaginous, and, in swelling, push apart 

 four lid-cells which, till then, close the upper end of the neck- 

 canal. The venter possesses a wall (one-layered in Liverworts, 

 Fig. 154, B, two-layered in Mosses), enclosing a large naked 

 ovum (e.), with a small ventral canal cell (v,) at the base of the 

 neck. The venter is borne on a short ~t^< which is rather 

 more massive in Mosses than in Liverworts. 



In Mosses, where they are interspersed with sterile hairs, 

 and in most leafy Liverworts, the archegonia occur in groups 

 at the top of the stem or its branches. They are enveloped by 

 a number of " involucral " leaves which generally differ in size, 

 and sometimes also in shape and colour, from the ordinary 

 leaves ; in most Mosses, however, such archegonial groups are 

 scarcely distinguishable from the ordinary leaf-buds. In some 

 leafy Liverworts (e.g. Lophocolea) the leaves of the involucre are 

 fused together, almost to their tips, to form a cup. 



In some of the thalloid Liverworts (e.g. Pellia) the archegonia 

 are found at the front end of the thallus, where they occupy 

 depressions roofed over by a scale-like involucre (Fig. 154, A, *'.). 

 In other cases (e.g. Marchantia, Fig. 146, G) they are situated 

 on special stalked star-like upgrowths which are divided into 

 4-10 lobes ; the archegonia in these cases form groups on the 

 lower surface, between the lobes, each group being enclosed 

 between a pair of involucral scales. 



The diverse forms of involucre surrounding the archegonia 

 not only protect them from desiccation, but form capillary 

 chambers tending to retain water. This facilitates the move- 

 ment of the sperms in fertilisation, which only takes place when 



