POLTPODIUM VULGARE 



The taxonomic conclusions for Europe would therefore seem to be that we are dealing 

 with three distinct though closely related species of which the third, the hexaploid, is 

 compounded of the other two and of very recent origin. The only point of uncertainty 

 concerns their names. There is apparently some doubt as to the nature of Linnaeus 

 type specimen since none is included in the Linnean herbarium, and it appears certain 

 that the name senatum could not be accepted as a specific epithet since it has already 

 been used for an entirely different species of Polypodium. This matter may therefore 

 perhaps be laid before professional systematists and decision deferred as to nomen- 

 clature, since to act otherwise incurs grave risk of encumbering the literature with 

 invahd epithets which might later have to be changed. 



■■*■ •/ ■•• v.-' 





Fig. 139. Meiosis in triploid Polypodium from a wild hybrid believed to be between tetraploid and 

 diploid. From the foot of the Pyrenees near Perpignan. Permanent acetocarmine. x 1000. 

 Almost all the chromosomes unpaired (3/2= 1 1 1). 



There is, however, a little more to add to the cytological story. I have been fortunate 

 in receiving from friends and correspondents some living wild material from both sides 

 of North America. Fig. 141 shows a whole plant, natural size, of P. virginianum from 

 Nova Scotia. Its general resemblance to the tetraploid of Europe is striking, although 

 its identity as P. virginianum is attested by the possession of the very characteristic 

 paraphyses (Fig. 142) only encountered in eastern America. Cytologically this plant 

 is, however, diploid, and the same is true of specimens attributable to P. vulgare var. 

 occidentale Hook, received from Vancouver Island and the Rocky Mountains, one leaf of 

 which is visible in Fig. 140 and the chromosomes in Figs. 143 and 144. Since it is im- 

 possible to equate 'var. occidentale' with 'var. senatum' or P. virginianum with the 

 European tetraploid, it seems probable that we shall have to accept at least two 

 American species in addition to the three of Europe. 



Lest, however, the reader should at this point lose patience thinking that only a 

 troublesome tangle of nomenclature is involved, it is perhaps worth pointing out the 

 extreme interest of the general situation which is beginning to become visible. In the 



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