168 THE OAK. 



Robur, but certain varietal forms of it have been distin- 

 guished, of which the commonest in this country are Q. 

 pedunculata^ a variety with the female flowers on long 

 peduncles, and Q. sessiliflora, with the female flowers on 

 short peduncles ; but although numerous attempts have 

 been made to define these forms, and while small differ- 

 ences in the petioles, lobing of the leaves, and the wood, 

 etc., have been insisted upon at various times by ob- 

 servers, it appears that the two varieties graduate into 

 one another by intermediate forms. In England, the 

 variety pedunculata is the commonest over the country 

 generally, but in the hilly districts of North "Wales and 

 the north of England the variety sessiliflora is said to 

 prevail. Similarly, on the Continent the latter variety 

 is found at higher elevations than the former, though its 

 area of occurrence is more restricted. This pronounced 

 variability of the oak was commented upon by the late 

 Charles Darwin, who points out, in the Origin of Species, 

 that more than a dozen species have been made by a 

 certain author out of what other botanists regard as 

 mere varieties of the common oak. 



De Candolle, who made a special study of this group, 

 found the variations so enormous that, although he 

 made something like 300 species, he decided that the ma- 

 jority of these were merely provisional ; and he conclud- 

 ed, as others have done, that we have, in the numerous 

 varieties of the species of this old genus Quercus, series 

 of incipient species. If the connecting forms were to 

 die out, leaving certain varieties more isolated than they 



