JURASSIC FLORA OF DOl'OLAS COUNTY, OREG. 121 



ficatioiis of Ihc ratlioi' polymorphous species Ginkgo (lifiitata (Bronsn.) 

 Heer. The hmits of variation in the same species, for leaves of the 

 Ginkgo type, are not fully known. Mr. Seward and Miss Gowan, in 

 their paper on diiikno hiloha:' have shown that the living Ginkgo ti-ee 

 is capable of considerable variation in its leaves, and that some of these 

 forms even r'eseinbl(> Jin-assic types. While foi-ms of the leaves of the 

 same sjiecies may lie s(>le('ted that would show such a variation, the 

 significance as fossils of ihi-se variant forms would be better understood 

 if it were known what proi)oilion in lumibers they b(>ar to the normal 

 forms and in what number they would occur in a foi'tuitous collection 

 of leaves produced by a fall from the same tr(M\ 



In the Oregon localities many portions of I'ock ar(> covered with 

 leaves of (Ufferent types in about equal proportions, indicating that 

 each type belonged to different trees, on which it was the predominant 

 foi'in of leaf. The great(>r numbei' of the Oregon Ginkgo leaves may 

 lie brought under several types of previously descril)ed forms. Rut 

 these may l)e connected by intermediate forms, which occur in con- 

 sideral)le numbers. Most of the previously described types illustrated 

 in the Oregon (Jinkgos are those given b>- Heer for th(> Jvu'assic of 

 Siberia. It will perhaps give a better idea of the Oregon forms if they 

 are described as belonging to the previously described species, which 

 they most resemble, treating under separate heads those that can not 

 be thus grouped. 



UixKuo DiGiTATA (Brunjiiiiart) Heer. 



Pi. XXX, Vlfr^. 1-7. 



l,S-2<). Sphirnnpteris latifoVui Pliill. [noii Broiign.] '' Geology of Yorkshire, pp. 148, 



1S9, pi. vii, fig. IN. 

 18.S0. ('iicJopteris (ligitatd Broiign.: Hi.st. Veg. Fos.s., Vol. 1, p. 21!l, jil. Ixi l)is, 



figs. ■_', :]. 

 l,s:{(). Adianiites digltatus (Broiigii.) Gopi).: Sy.st. Fil. Foss., p. 217. 

 ],S4:i. Haiera digitata (Brongn.) Fr. Br. in Minister: Beitr. z. Petrefacten-Kunde, 



Vok II, Heft VT, ]). I'l. 

 1865. Cyclopteris incisa Eiehw.: Letha-a Rossi('a, Vok II, p. 13, pi. iv, lig. G. 



" T\w maitlpiiliuir tree, l)y A. C. Seward uiul Miss .1 . ( Iciwun : Annals of Botany, Vol. XTV, No. LIIT. ^tarcli , 

 19()0, pp. 109-1.54, pi. vili x. 



'' Broiijjniart 's Carboniferous speeies Sphnwpleri.f Inlifnlia dates from tlie Prodrome (p. .'il ), one year earlier 

 than tliis, whieli is tliercfore to be dropped, although antedating all other names for this plant.— L. F. W. 



