No. 5.31] 



NOTES AND LITERATURE 



C91 



cate leaves of certain filmy ferns, for which these liverworts 

 might easily be mistaken. 



In the development of the sporophyte the Anacrogynee show a 

 decided advance over the Marchantiales. There may be devel- 

 oped a considerable amount of sterile tissue in the capsule, aside 

 from the ordinary elaters, and this sterile tissue sometimes 

 assumes the form of a sort of columella or " elaterophore, " sug- 

 gesting the columella found in the Anthocerotacese, and possibly 

 homologous with it. This elaterophore may be either apical 

 (Aneura) or basal (Pellia) . 



While recognizing the entirely independent origin of leaves in 

 several lines of the Anacrogynse, nevertheless Cavers is inclined 

 to believe that all of the true leafy liverworts (AcrogynEe) can 

 be traced back to a single type which he thinks is best repre- 

 sented by Fossnnihrx,i>fi. which genus he places at the top of the 

 series Codoniacea?. It may be said, however, that there are some 

 strong arguments in favor of a polyphyletic origin for the Acro- 

 gyna? — a view which has been defended by several students of 

 the group. 



There are, as we have already stated, good reasons for believing 

 that Fossombronia should not be associated with Pellia ami the 

 other Codoniacese, but associated with the Sphoerocarpales, as the 

 highest member of a series of which Sphcerocarpus and Geothal- 

 lus are lower members. This interpretation would not interfere 

 with the acceptance of Cavers 's view that some at least of the 

 leafy liverworts have been derived from forms like Fossombronia. 



The acrogynous Jungorinanniales. or leafy liverworts, include 

 much the larger part of existing liverworts. Of about 250 

 genera and 4,500 species of known liverworts, all but 60 genera 

 and 700 species belong to the acrogynous Jungermanniales. 

 They are nevertheless comparatively uniform in type, and Cavers 

 believes that they may all be traced back to a common ancestral 

 type allied to Fossombronia. 



With very few exceptions they show a single tetrahedral apical 

 cell and usually three series of leaves corresponding to the three 

 lateral faces of the apical cell. The ventral leaves (amphigas- 

 tria) are not infrequently absent, and both dorsal and ventral 

 leaves often show various modifications, among the most striking 

 of which are hollow sacs presumably developed for water storage. 



The tissues are very simple, and only very rarely is there any 

 specialization of cells for conduction or other purposes. In size 



