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to understand, as both the leaf and acorn are eminently fitted to 

 terminate one extreme of the series of which Phellos is the other, 

 as I have endeavored to show in the accompanying plates. The 

 only cause for hesitation which I have in accepting this as a satis- 

 factory conclusion is that I failed to find trees of rubra growing in 

 the immediate vicinity, although there are a number of them only 

 a few hundred yards away. We should however remember that 

 this species may have been present, associated with Phellos, years 

 since, at the time when the existing large specimens of heterophylla 

 were produced, probably 50 or 75 years ago. It may be that 

 hybridization has not taken place in many years and that the 

 young trees are merely seedlings from a few originals. This idea 

 is strengthened in my mind from the fact that the largest and 

 oldest trees come nearest to the type of rubra, while the smallest 

 or youngest trees show a preponderance of the Phellos type — ap- 

 parently showing a tendency to revert back to it. Dr. N. L. 

 Britton has also pointed out to me a significant fact in this con- 

 nection, viz. : that throughout the region where heterophylla has 

 been found Phellos, rubra, and other members of the black oak 

 group occur, but that to the eastward, in the Pine Barren region, 

 heterophylla or rubra are not reported, although Phellos is abun- 

 dant and palustris and other black oaks are present In fact 

 heterophylla only seems to occur where Phellos and rubra occupy 

 a territory in common. 



