168 THE OAK 
The latter is denominated botanically as Quercus 
Ttobur, 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. sessilijlora, 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, 
&e., 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 800 species, he concluded that 
the majority of these were merely provisional; and he 
concluded, as others have done, that we have in the 
numerous varieties of the species this old genus Quercus, 
series of incipient species. If the connecting forms 
