RELATIONSHIPS OF THE OAKS 169 
were to die out, leaving certain varieties more isolated 
than they are at present, systematists would elevate the 
latter to the rank of species. 
It is interesting to observe that twenty-eight varie- 
ties of the common English oak (Q. Robwr) have been 
described, and that the majority of these can be grouped 
around the three forms pedunculata, sessiliflora, and 
pubescens, the latter being a somewhat hairy variety 
found on the Continent. No doubt we have here, again, 
a case where the three varieties mentioned would be 
accorded specific rank if the connecting forms died out, 
as some of them appear to be doing. 
I have already stated that the oaks are a very 
ancient family, and their great variability is im accord- 
ance with this. It probably implies that the genus has 
had time during its migrations over the Northern Hemi- 
sphere to vary immensely, and that some of the varie- 
ties have become adapted to given situations, others to 
others. On the whole, the oak family must be regarded 
as a northern type which has sent extensions south- 
ward. 
Now let us glance at their geological history. Some- 
thing like 200 forms of fossil oaks have been described 
from remains, chiefly of leaves and wood, found in 
various parts of the world. Some of the European fossil 
forms remind us of species now found only in hot 
countries near the tropics, others are peculiar, and some 
are very doubtful, 
The earliest remains of oaks come from the Creta- 
