6 BERRY— A POSSIBLE EXPLANATION 



Temperate Zone. I regard it, in fact, as sub-tropical. Space does 

 not permit a discussion of the range of the existing representatives 

 of this Jackson flora. This is done in the pubhcation cited above, 

 and the generic names mentioned will serve those of my botanical 

 readers who wish to check my conclusions. Now, let me compare 

 this Jackson flora with the so-called Kenai flora of Alaska.^ 



The Kenai flora, as published, consists of about 120 species. The 

 most abundant forms are willows, oaks, poplars, walnuts, beeches, 

 birches, hazels, and alders — distinctly Temperate, and cool rather 

 than warm Temperate types. Perhaps the most abundant plants indi- 

 vidually, certainly the widest ranging geographically in northern lati- 

 tudes (Holarctica), are the leaves of hazel bushes (Corylus). Of 

 the 54 genera of Knowlton's list, the following nine are not present 

 in the existing flora of North America : Ginkgo, Glyptostrobus, Tax- 

 ites, Hedcra, Pal'mrus, Elcsodendron, Pterosperinites, Trapa, and 

 Zizyphus. 



It may seem that I am juggling the evidence in omitting these 

 nine genera from further consideration, but let me point out that the 

 three of these about which there seems to be no doubt regarding their 

 identity, namely, Ginkgo, Trapa, and Glyptostrobus, are all Temperate 

 types in the existing flora. The remaining six genera are under more 

 or less suspicion of quite a different order from any differences of 

 opinion among paleobotanists regarding the identification of the hazels, 

 birches, alders, etc., with which they are associated. Opinion might 

 differ as to whether a particular species of the latter was a Betula or 

 Alnus, an Ulmus or a Carpinus, or a Planera; or whether one or 

 several species of Corylus should be recognized as distinct species; 

 but opinion is unanimous that the choice is thus narrowed, whereas 

 in the case of such things as Taxites — all any one knows is that it 

 represents some Conifer. Why waste time trying to explain the cli- 

 matic significance of Paliurus, a mostly extinct genus, when the par- 

 ticular fossil is probably not a Paliurus; or why concern oneself with 

 an Arctic species of Zisyphus when the form in question is probably 

 a Ceanotlms? I ask, can any one prove that the form-genus Ptero- 



3 As listed by Knowlton in 1919. Hollick's extended labors on this flora 

 which may be expected to contain some new species, will undoubtedly 

 modify, but will not alter the force of the present comparison. 



