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 



V. 



KK,. nS. 



A = archegoniiim of R ice ia trichocarpa showing ventral canal cell (z>) and ovum. 

 j5 = ripe archegonium of Riccia glaucii. X 260. (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 Riccia ; but it may be assumed from 

 analogy with other Liverworts that it takes place here also. It is, howe\vi, 

 recorded by Garber 1 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 Riccia thus described is the simplest sporophyte 

 known among the Archegoniatae. It has been habitually regarded as a 



1 Bot. Gaz., 1904, p. 171. 



