84 STUDIES IN FOSSIL BOTANY 



for example, Equisetites Burchardti from the Wealden, 

 had tubers just like those of some recent species. 



The genus Phyllotheca, very similar to Annularia, 

 but with the leaves more united, appears to represent a 

 Palaeozoic type which extended into the Mesozoic 

 period as far as the Lower Jurassic. Sckizoneura, a 

 characteristic Triassic genus, is remarkable for the 

 splitting of the leaf-sheath into leaf-like segments of 

 variable width. The Secondary Equisetales appear to 

 offer a promising field for research. Professor Nathorst 

 kindly informs me that M. Halle, who is investigating 

 the Stockholm collections of Rhaetic and Liassic 

 Equisetaceae from Scania in Sweden, has succeeded in 

 finding the sporangia on the lower surface of the 

 peltate sporangiferous scales ; this is the first time 

 they have been observed in Mesozoic specimens. The 

 sporangiophores, which appear to have been of an 

 almost ligneous texture, have on their lower surface 

 the prints of about twenty-four sporangia — a larger 

 number than in the recent genus. The sporangia and 

 spores closely resemble those of the recent Equisetum ; 

 the elaters, however, are not preserved. An interesting 

 point is that the spores show a triradiate marking 

 almost identical with that on the spores of C alamo stachys 

 Binneyana (cf. Fig. 22, D). 1 



From the rapid sketch of the fossil Equisetales 

 which has now been given, it is evident how greatly 

 our whole idea of the family is widened by the study 

 of the extinct forms. It is from these alone that we 



1 At present M. Halle has only published a preliminary notice, in 

 Swedish, of his interesting discoveries. 



