l8 9i.] * Relationships of the Archegoniata. 325 



j 



Ma rch 



as the most primitive of living forms, and not the Ricciaceae, 

 which are usually so considered. It seems more likely that the 

 latter, together with the very closely related Marchantiaceae, 

 represent a group in which the thallus has become highly dif- 

 ferentiated, without a corresponding development of the spo- 

 rophyte, and which reaches its highest expression in such 



intia and Asterella. Of course it is possible 

 to regard the simpler Ricciaceae as the primitive forms from 

 which the Jungermanniaceae have sprung; but this would in- 

 volve a reduction of the thallus in the latter which seems 

 hardly probable, as in some Marchantiaceae, and probably in 

 the Ricciaceae also, the young thallus corresponds closely to 

 to that of the simpler Jungermanniaceae, and the massive 

 thallus of the older plant arises secondarily. The very sim- 

 ple sporogonium of Riccia, of course, is an important point 

 in determining its systematic position, and indicates, that if, 

 as here suggested, the Ricciaceae are derived from forms like 



the lower Jungermanniaceas, it must have been at a very 

 early period, before the sporogonium of the latter had reached 

 its present stage of development. 



Leitgeb 1 has already called attention to the connection of 

 Ant/wceros with the Jungermanniaceae, and the evolution of the 

 foliose forms of the latter group from the thallose forms is 

 easily demonstrated. 



We may then pretty safely assume that the primitive liver- 

 worts were thallose forms not unlike such existing forms as 

 Mctzgeria, or the prothallium of an Osmunrfa, and that from 

 these, three stocks diverged, the Ricciaceae (including Mar- 

 chantiaceas), the Anthoceroteas, and the foliose Jungerman- 

 niaceae The first and third of these groups forming the great 

 bulk of the livins" forms are to be regarded as specialized 



branches that end blindly; the second, however, is especially 

 important from a morphological standpoint, as it probably 

 represents to a considerable degree, the ancestral form from 

 which both the true mosses and the Pteridophytes have sprung. 

 The Anthoceroteae 2 differ remarkably from the other liver- 

 worts, especially in the development of the highly specialized 

 sporogonium. This finds its nearest homologue, not among 

 the Hepaticae, but in the lowest order of the true mosses, viz.: 



1 Untersuchungen liber die Lebermoose, Vol. V, pp. 8-9. 



2 Leitgeb, 1. c. 



