258 BRYOPHYTA 
spores so that at maturity they are not to be recognised. A similar fate 
is described for the cells of the inner layer into which the archegonial 
wall has meanwhile divided; and thus there is a supply of nutritive 
material to the developing spores, comparable to that from the tapetum in 
the higher Archegoniatae. The cells that lie within become rounded off, 
and thus separate from one another in the enlarging fruit (Fig. 120): all 
of them undergo the tetrad-division, and develop into spores, which have 
Fic. 118. 
A =archegonium of Riccia trichocarpa showing ventral canal cell (v) and ovum. 525. 
B=ripe archegonium of Riccia glauca. X260. (After Campbell.) 
a thick, darkly coloured outer wall. These are set free by the dis- 
organisation of the archegonial wall, or calyptra, the outer layer of which 
persists till the spores are ripe. Under suitable conditions the spores 
germinate, and each forms a new gametophyte. 
Hitherto no observations have been described as to the reduction of 
chromosomes in the tetrad-division of Azccéa; but it may be assumed from 
analogy with other Liverworts that it takes place here also. It is, however, 
recorded by Garber’ that the number of chromosomes in the gametophyte 
of Ricciocarpus natans is four, while in the sporophyte it is eight; but 
the actual fact of reduction in the tetrad-division was not observed. 
The sporophyte of Azccia thus described is the simplest sporophyte 
known among the Archegoniatae. It has been habitually regarded as a 
1 Bot. Gaz., 1904, p. 171. 
