1 8 MOSSES AND FERNS chap. 



before the body of the spermatozoid is complete. Usually 

 when the spermatozoid escapes, it has attached to the coil a 

 small vesicle which swells up more or less by the absorption 

 of water. This vesicle is the remains of the cytoplasm of 

 the cell, and may, perhaps, contain also some of the central 

 part of the nucleus. Guignard ^ asserts that sometimes the 

 cytoplasm is all used up during the growth of the spermatozoid, 

 and that the free spermatozoid shows no trace of a vesicle. 



In the Ricciacese and in SpJicerocarpus new archegonia 

 continue to form even after several have been fertilised, so that 

 numerous sporogonia develop upon the same branch of the 

 thallus ; but in most Liverworts the fertilisation of an arche- 

 gonium checks the further formation of archegonia in the same 

 group, and only those that are near maturity at the time reach 

 their full development ; and even if more than one archegonium 

 of a group is fecundated, as a rule but one embryo comes to 

 maturity. 



Unquestionably the lowest type of sporogonium is found 

 in Riccia (Fig. 6). Here the result of the first divisions in 

 the embryo is a globular mass of cells, which a little later shows 

 a single layer of peripheral cells and a central mass of spore 

 mother cells, all of which produce spores in the usual way. The 

 sporogonium remains covered by the venter of the archegonium 

 until the spores are ripe, and never projects above the surface 

 of the thallus. The spores only escape after the thallus (or at 

 ■least that part of it containing the sporogonia) dies and sets 

 them free as it decays. In the genus SpJicEvocarpus (Fig. 30), 

 which may be taken to represent the next stage of development, 

 we notice two points in which it differs from Riccia. In the 

 first place there is a basal portion (foot), which is simply an 

 absorbent organ, and takes no part in the production of spores. 

 Secondly, only a part of the archesporium develops perfect 

 spores. A number of the spore mother cells remain undivided, 

 and serve simply to nourish the growing spores. In the 

 majority of the Hepaticse the sporogonium shows, besides the 

 foot and the capsule, an intermediate portion, the stalk or seta, 

 which remains short until the spores are ripe, when, by a rapid 

 elongation of its cells, the capsule is forced through the calyptra 

 and the spores are discharged outside. In these forms, too, 

 some of the cells of the archesporium remain undivided, and 



^ Guignard (i), p. 66. 



