166 COBB— RELATIONSHIPS OF WHITE OAKS [April 23, 



and one in New Zealand (ranges separated by the Pacific). Cas- 

 tanopsis (the less specialized chestnuts) is limited to southeast Asia, 

 except for two Calif ornian species (ranges separated by the Pacific). 

 Castanea is present in southeast Asia, North America and Europe. 

 Quercus has most numerous species in southeast Asia and (espe- 

 cially) Mexico and Central America (regions separated, again, by 

 the Pacific), while the subgenus Cyclobalanopsis is limited to south- 

 east Asia (monsoon province). In consideration of the facts that 

 the most primitive genus still lingers on the two sides of the south- 

 ern Pacific, and that so many other groups are found only in regions 

 bordering on the northern Pacific, it is more than plausible that the 

 family Fagacese originated in the Antarctic-Pacific region, and 

 moved northward towards its present northern-hemisphere distribu- 

 tion in the region of the Pacific Ocean. This of course involves 

 the hypothesis of an ancient Cretaceous or pre-Cretaceous Pacific 

 continent — for which there is much other distributional evidence 

 and which Scharff,^ among others, holds to be highly probable. The 

 broad similarity of the ranges of Pasania, Castanopsis and Cyclo- 

 balanopsis was undoubtedly determined at this early time. The 

 problem of the extension of certain species of Fagus and Castanea 

 to Europe seems entirely separate, and probably belongs to a more 

 recent period. Quercus is involved with both the older and the 

 more modern distribution ; they have been mapped out here for con- 

 venient reference in the coming discussion of Quercus. 



II. History of Quercus, Hypothetically Reconstructed. 



Oaks, living or fossil, have been reported from every continent. 

 Living species, however, are unknown in the southern hemisphere, 

 except that they are found south of the equator in the East Indies, 

 and among the mountains of Ecuador (localities separated by the 

 Pacific). Species, as was said, are most numerous in Mexico and 

 Central America and in southeast Asia ; the subgroup Cyclobalanop- 

 sis is limited to southeast Asia. Remembering that Pasania and 

 Castanopsis are almost limited to the same region, and that the 

 pasania-chestnut-oak group of the Fagacese shows here a concen- 

 tration, and a profusion of species, seen nowhere else in the world, 



2 Scharff, " Distribution and Origin of Life in North America." 



