1L*<; MESOZOK" FLORAS OF UNITED STATES. 



Leaves. — Xuiiierous s| )ocii I loiis of (iinkgos occui- in the Oregon 

 flora that soniotinies h-dvv llie character of the form called l)v Heer 

 G. sibirica and sometimes of his (i. SclnnidlidiKi." tlie latter l)eing a 

 smaller leaf with a smaller mmiber of segments; hut these graduate so 

 often one into the other, by commonly occm-ring intermediate forms, 

 that there is no satisfactory way of separating them. 1 will therefore 

 discuss them as one species. As the sibirica form is the most common, 

 and apparently the type, I will regard them all as variations of (r. sibirica. 

 This Ginkgo is the most abundant and widely diffused type in the Oregon 

 Jurassic, the leaves sometimes thickly covering the surface of the rock. 

 If we neglect the intermediate shapes it is true we may select forms that 

 are pretty widely separated, either as G. sibirica or as G. Schmi'dtiana. 

 This is possibly what Heer did, not having so many specimens to illustrate 

 the passage forms. In the description I will first note those l)elonging 

 to G. sibirica proper and distinguish the smaller leaves as being of the 

 Schmicltiana form. Possi):)ly the latter may be immature leaves of the 

 former. The normal or true sibirica type of Ginkgo in the Oregon 

 Jurassic has the following character: The texture of the leaf is decidedly 

 thinner than that of any of the other types except that of G. Schmicltiana. 

 The leaves are small, being sometimes about the same size as those of 

 G. (ligitata, but generally smaller. The segments of ultimate order are 

 numerous, slender, and formed by a deep incision of the leaf, but not so 

 deep as in G. lepida. These segments are narrowly elliptical or linear in 

 form and widest near their middles, but do not vary much in width 

 throughout their length. 



PI. XXXIII, Fig. 1, gives a portion of a leaf with numerous narrow 

 segments. Fig. 2 shows the basal part of a medium-sized leaf, with a 

 portion of the petiole well preserved. Fig. 3 gives one of the largest 

 sized leaves, but in a fragmental condition. This is shown much enlarged 

 in Fig. 4. Fig. 5 depicts a portion of a medium-sized leaf, with a central 

 segment, well preserved. This is also shown much enlarged in Fig. 6. 



" I'l. Foss. Arct., Vol. IV, Pt. II, p. 60, pi. vii, fig. 5; pi. xiii, figs. 1-2. I have not put Ginkgo Schmidtiana 

 ill tlu! synonymy of G. sibirica, althmigli Pnifcssor Fontaine clearly indicates that tlic Oiogoti forms embrace 

 Ixjtli of Ilecr's species and show all the necessary conncctiiif; links. As Heer de.scrihed G Sehnndtinna on p. 60 

 and G. sihirica on p. fil of his work, if they are consohdaled the resulting species would, by the rules, become 

 G. Schmidtiana and not (!. .liliirica. This nia_v .vet have to be done, but rather than do it I prefer to regard the 

 species as distinct, and tlie .\merican forms approaching G. SchiniJtiana as representiug the range of variation 

 of tlic [lolyjiiorplious species G. sibirica. — L. K. W. 



