PALEOBOTANY BERRY. 307 



morphological considerations, the evidence that the Osmundales con- 

 stitute a relatively primitive line of fern evolution is furnished by 

 impressions like Todea Lippoldi Stur from the Lower Carboniferous 

 of Silesia, petrified sporangia such as Todeopsis primaeva Renault 

 from a similar French horizon, or Sturiella from the German Upper 

 Carboniferous, and finally by the phylogenetic series of petrified 

 stems described by Kidston and Gwynne Vaughan, among which the 

 genera Bathypteris, Anomorrhoea, Thamnopteris, and Zalleskya come 

 from the Upper Permian (Thuringian) of the Ural region. Space 

 does not permit a description of their histology, but it may be pointed 

 out that the order appears to have been derived from an ancestor 

 with a solid stele like the Coenopteralian species Diplolahis Roem< ri 

 and to have undergone an evolution more or less paralleling that of 

 the Z}'gopteraceae. This line is continued by Jurassic and Lower 

 Cretaceous species of Osmundites from South Africa, New Zealand, 

 and Canada, and by Tertiary species from England, South America, 

 and Hungary. Impressions of both sterile and fertile fronds allied 

 to Todea are abundant and cosmopolitan in the late Triassic and 

 Jurassic and continue into the Cretaceous, while Osmunda-like frond 

 forms are common throughout the Lower and Upper Cretaceous and 

 Tertiary in all parts of the world. 



A class of ferns, including the existing heterosporous Rhizocarps, 

 or so-called water ferns, includes the order Hydropterales and pos- 

 sibly an extinct order, the Sagenopterales. The two existing fam- 

 ilies, MarMliaeeae and Salviniaceae, are small, more or less wide- 

 spread aquatic forms with dioecious prothalli, exannulate sporangia 

 inclosed in " sporocarps,' 1 which are modified frond segments or 

 highly developed indusia,. Only a single megaspore reaches matur- 

 ity in each megasporangiimi. The Salviniaceae contain the genera 

 Azolla and Salvinia with between 15 and 20 existing species of the 

 warmer regions and the leaves of the latter genus not appreciably 

 different from those of the existing species are found throughout 

 the Tertiary period. 



The Marsiliaceae consist of three genera — the monotypic Brazilian 

 Regnellidium, Pilularia with about six species and Marsilia with over 

 50 widely distributed existing species. The last has been found fossil 

 as early as the Upper Cretaceous, but is rare and more or less un- 

 certain in the fossil state. The extinct genus Sagenopteris is based 

 for the most part on groups of two to five large asj^mmetrical reti- 

 culate veined pinnules borne digitately at the apex of a long and 

 rather stout stipe and found as impressions in the late Triassic 

 (Keuper and Rhaetic) very common in the late Triassic and basal 

 Jurassic (Liassic) with seven or eight species rather widespread 

 during the Lower Cretaceous and surviving in one or two Upper 



