xxiv] 



FOSSILS 



times (Fig. 493). Seward, however does not consider the evidence as con- 

 clusive (Hooker Lecture, 1922). The sorus is certainly of the Gleicheniaceous 

 type, and the sporangia closely re- 

 semble those o{ Dicranopteris, but it is 

 a question whether the annulus con- 

 sisted of a single row of cells. Still 

 this in itself is not distinctive, for 

 Stromatopteris occasionally has an 

 irregularly double annulus, and the 

 like is sometimes seen in Gleidienia. 

 Moreover, if the Zygopterid sporangia, 

 with their broad annular band, represent 

 a prototype of later Fern-sporangia, 

 we should expect intermediate forms 

 to show irregularities such as Oligo- 

 carpia appears to present. (See 

 Kidston, ii, 4, p. 284.) But further, a 

 specimen of Oligocarpia shown me by 



!*'§• 493- Sorus of Oligocarpia Gutbieri 

 Goppert, from a photograph by the late Dr R. 

 Kidston. The annulus had the appearance of 

 being a single series of cells. It was difficult 

 on examination of the specimen to be sure there 

 was no synangial fusion, but the presence of 

 the annulus would make fusion appear to be 

 improbable, as the annulus would then be 

 functionless. 



the sorus was synangial. If it were 

 so, which is doubtful since each 

 sporangium is annulate, this again does 

 not rule out a Gleicheniaceous affinity, for in the Marattiaceae synangial 

 sori exist {Danaea, Marattia), while others have separate sporangia {Angiop- 

 teris, etc.). Moreover occasional synangia occur in modern Gleicheniaceae. 

 The conclusion thus appears to be justified that fossils, having characteristic 

 featuresshowing a general resemblancetothoseof the Gleicheniaceae, certainly 

 existed in the Coal Measures. But it is only in more recent geological time 

 that the clear proof of the occurrence of Ferns definitely referable to the 

 Family is forthcoming. 



The oldest examples of authentic Gleicheniaceae are from the Keuper of 

 Switzerland. From this period onwards, through the Jurassic to the Chalk, 

 frequent records show that the Gleicheniaceae were widely distributed: but 

 it is in the Cretaceous floras that the genus was especially abundant, 

 extending even to West Greenland. In the Wealden of Belgium the recog- 

 nition of the type is further supported by the discovery of rhizomes having 

 the characteristic stelar structure (Bommer, Seward). Though it must 

 therefore be admitted that the recognition of the Gleicheniaceae as definitely 

 a Palaeozoic Family is doubtful, still it is certain that they already existed 

 in early Mesozoic times, and flourished in the Chalk Period. Their record 

 is very like that of the Schizaeaceae. Both families had already acquired 

 in early Mesozoic time those characteristics by which the}' are recognised 



14—2 



