RELATIONSHIPS OF THE OAKS. 169 



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. Robur) 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 in accordance with 

 this. It probably implies that the genus has had time 

 during its migrations over the Northern Hemisphere to 

 vary immensely, and that some of the varieties have be- 

 come adapted to given situations, others to others. On 

 the whole, the oak family must be regarded as a north- 

 ern type which has sent extensions southward. 



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 vari- 

 ous parts of the world. Some of the European fossil 

 forms remind us of species now found only in hot coun- 

 tries near the tropics, others are peculiar, and some are 

 very doubtful. 



The earliest remains of oaks come from the Creta- 

 ceous strata, being coeval with the first undoubted dico- 

 tyledons that have been found. Many have been found 



