POLTPODIUM VULGARE 



The commonest form of Polypodium in most parts of western Europe from the north of 

 Scandinavia to the Pyrenees is the tetraploid. This is shown photographically in 

 Fig. 130^ and in silhouette in Fig. 135 c. It possesses characteristically the narrow 

 outline for which the crude woodcut of the Ortus Sanitatis might be taken as a 

 rough diagram. Many details of the shape of the pinnae are variable, but two fairly 

 constant characters are the circular, as opposed to oval, sori and the number of indurated 

 cells in the annulus. Attention was first drawn to the usefulness of this last character by 

 Farquet in 1933 with special reference to P. vulgare var. serratum (Willd.) Milde to be 



Fig. 131. Polypodium pinnae enlarged to twice natural size to show the shapes of the sori. a. The French 

 diploid, sori oval. b. The tetraploid, sori round, c. The hexaploid, from a rather small frond, 

 sori oval. 



described below, and our experience strongly confirms his. In tetraploid Polypodium 

 the range of numbers is from 11 to 13 cells with 1 2 as the commonest number. 

 A sporangium showing this is reproduced in Fig. 132. 



In contrast to the tetraploid the diploid, which corresponds in our experience with 

 descriptions of P. vulgare var. serratum wherever we have found it, is of characteristically 

 southern affinities. It appears to be the only type present at low altitudes in the Medi- 

 terranean basin. Living material has been cytologically examined by us from two places 

 in the south of France (Pont-du-Gard and Perpignan) and from north Italy while 

 herbarium records extend the range at least as far as North Africa and the Atlantic 

 Islands (Madeira, Teneriflfe, etc.). In northern Europe it is found in discontinuous 

 patches, usually on limestone and often in districts containing other species of southern 

 origin. Examples of such localities from which we have already obtained it are the 



132 



