V] FERNS 79 



is another point which may have a bearing in this 

 question of antiquity, namely the fact that the spores 

 of Osmunda are green and do not possess the powers 

 of indurance inherent in the spores of the majority of 

 ferns which are not green. It has recently been con- 

 tended by Professor Campbell of Stanford University 

 that the delicate green spores of the Liverworts, 

 plants closely allied to the Mosses, constitute an 

 argument in favour of the antiquity of these plants (46). 

 Certain Liverworts are cosmopolitan in their range, 

 e.g. the genera Riccia and Marchantia. 



If certahi genera are widely distributed, notwith- 

 standing the fact that their reproductive cells, by 

 which dispersal is effected, are ill-adapted to withstand 

 unfavourable conditions or to endure prolonged 

 desiccation, it would seem reasonable to conclude 

 that their emigration has been accomplished slowly 

 and with difficulty. Ferns such as Osmunda, with 

 green and short-lived spores, would thus be handi- 

 capped in competition with other genera provided 

 with more efficient means of dispersal and better 

 equipped for the vicissitudes of travel. 



The inferences as to antiquity deduced from a 

 study of the existing species of Osmunda and Todea 

 receive striking confirmation from the testimony of 

 fossils. Some of the oldest known Palaeozoic ferns, 

 though differing too widely from the existing Osmundas 

 and Todeas to be included in the same family, afford 



