356 



ANNUAL REPORT SMITHSONIAN INSTITUTION, 1918. 



or has any phylogenetic significance. Similarly the paired sporangia 

 appear to represent a reduction from the more numerous sporangia 

 in the Mesozoic species. 



The modern Ginkgo has a persistent primary cambium, collateral 

 bundles, double-leaf trace, no wood parenchyma, resin ducts in both 



■ 



Fig. 21. — Views illustrat ing the variat ion in leaf form of the fossil species of Ginkgo. 



1. Ginkgo digitata (Brongn.) Heer. Jurassic of Oregon. 



2. Ginkgo laramiensis Ward from the Upper Cretacecus of Wyoming. 



3. Ginkgo obtrutschewi Seward. Middle Jurassic of Chinese Dzungaria. 



4. Ginkgo sibirica Heer. Jurassic of Oregon. 



5. Ginkgo huttoni magnifolia Fontaine. Jurrassic of Oregon. 



6. Ginkgo adiantoides (Unger) Heer. Tertiary of Isle of Mull. 



7. Ginkgo adiantoides from the Fort Union of Montana. 



pith and cortex, tracheids with radial opposite pits separated by so- 

 called bars of Sanio. The leaves are comparable anatomically with 

 those of cycads but are simple and deciduous. They are borne on 

 either long terminal shoots or in tufts at the apex of short axillary 

 shoots, the latter habit shared by some fossil species of Baiera. The 



