126 MESOZOIC FLORAS OF UNITED STATES. 



Leaves. — Numerous specimens of Ginkgos occur in the Oregon 

 flora that sometimes have the character of the form called by Heer 

 G. sihirica and sometimes of his G. Schmidtiana," the latter being a 

 smaller leaf with a smaller number of segments; but these graduate so 

 often one into the other, by commonly occurring intermediate forms, 

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

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

 and apparentlj^ the type, I will regard them all as variations of G. sihirica. 

 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. sihirica or as G. Schmidtiana. 

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

 the passage forms. In the description I will first note those belonging 

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

 Schmidtiana form. Possibly the latter may be immature leaves of the, 

 former. The normal or true sihirica 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. Schmidtiana. 

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

 G. digitata, 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. 



PL 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. 



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

 in the synonymy of G. sihirica, although Professor Fontaine clearly indicates that the Oregon forms embrace 

 both of Heer's species and show all the necessary connecting links. As Heer described G. Schmidtiana on p. 60 

 and G. sihirica on p. 61 of his work, if they are consolidated the resulting species would, by the rules, become 

 G. Schmidtiana and not G. sihirica. This may yet have to be done, but rather than do it I prefer to regard the 

 species as distinct, and the American forms approaching G. Schmidtiana as representmg the range of variation 

 of the polymorphous species G. sihirica. — L. F. W. 



