172 COBB— RELATIONSHIPS OF WHITE OAKS [April 23, 



several reasons for marking off rather sharply durandii and brevi- 

 loba from the remainder of the species present in this area, and 

 for suggesting the possibihty that they may be a relic from the time 

 of the dift'erentiation of this deciduous section of Leucohalanus. 



The remainder of the group has a very wide range. It touches 

 the Rockies in Canada, and reaches Texas, Florida, and Maine. 

 Nevertheless, it is almost true to say that every one of the species 

 includes in its range the region of the southern Alleghanies. This 

 region certainly seems to have been a center of distribution after 

 the retreat of the ice fields, for this as well as for certain other 

 groups of plants and animals {Cambarus, and the Unionidse, for in- 

 stance). The present distribution must have been largely achieved 

 by the Pleistocene, for late Pleistocene fossils indicate a range 

 broadly similar to that of the present. 



The species, aside from (i) durandii and hreviloha, fall into 

 three main groups— (2) macro car pa group, (3) minor group, (4) 

 prinus group. Their relation to one another is not entirely clear. 

 The macrocarpa group in some ways holds a central position, which 

 suggests that it may be the oldest. So do the persistent stipules of 

 all members of the group; this is without any doubt a primitive 

 character. Its species moreover have the widest range, macrocarpa 

 extending in the north to Saskatchewan and Maine, and in a great 

 southward curve with its lowest point well down the Mississippi 

 Valley ; south of this it is replaced by lyrata. Again, Tertiary leaf- 

 prints which have been referred to deciduous Quercus are limited 

 thus far to types resembling lyrata and minor. (Cockerell's species 

 lyratiformis from the Florissant beds is now reported from the 

 John Day Basin, Oregon, where Knowlton also recognizes leaves of 

 the type of minor.) There are so many suggestions of this sort 

 that at present we must assume the macrocarpa group to be nearest 

 to the ancestral type ; and, though the fruit is aberrant, lyrata may 

 well stand near the base of the group. 



The ininor group, or at least minor itself, has some affinities with 

 bicolor and macrocarpa. Its wide range and the Tertiary occurrence 

 of this or a similar species show that it has valid claims to antiquity. 

 Whether alba belongs in this group is uncertain ; it is difficult to 

 see reasons for connecting it closely with any other species. Mar- 



