62 



GINKGODItJM AND CZEKANOWSKIA 



[CH. 



deep median sinus into divergent obtuse segments (fig. 659). One 

 leaf is described as 6-6 cm. long, 2-1 cm. broad with thirty veins 

 and an interstitial ' vein ' between 

 each pair : the interstitial ' vein ' 

 is due to the presence of an inter- 

 costal stereome strand. Thomas^ 

 records this species from the 

 Bathonian series of Kamenka 

 in the south of Russia (fig. 659, 

 B). The specimens from Alaska 

 named by Fontaine^ Ginkgodium? 

 alaskense agree more closely with 

 Ginkgoiies. 



CZEKANOWSKIA. Heer. 



Fig. 659. Ginkgodium Nathorsti. (Nat. 

 size; A, after Yokoyama; B, after 

 Thomas.) 



Heer^ gave this name (after 

 Czekanowski who discovered the 

 specimens) to fascicules of long 

 and narrow, filiform, leaves with a simple or occasionally 

 forked lamina borne on a short supporting axis covered with 

 broader and shorter scale-leaves. The deciduous fascicules or 

 dwarf-shoots are similar to those of Phoenicopsis. Bunches 

 of Czekanowskia leaves with their short scale-covered supporting 

 axes resemble the dwarf-shoots of Pines*. Heer assigned to this 

 genus some seeds associated with the leaves, also what he beheved 

 to be a male flower^, an example of a reproductive shoot of the 

 type described on page 57 as Stenorachis. There is, however, 

 no conclusive evidence as to the nature of the reproductive organs. 

 The venation is seldom shown on the carbonised laminae; some 

 leaves are finely striated while on others there may be one or two 

 narrow ridges that represent veins, but as a rule the impressions 

 afliord no indication of the venation. Czekanowskia was placed 

 by the author of the genus in the Ginkgoales, the short shoots 

 being compared with those of Ginkgo though, except in the larger 

 number of the leaves, they closely resemble the foliar spurs of 



1 Thomas (11) p. 75. PI. iv. figs. 9—11 ; PI. vm. fig. 3. 



2 Fontaine in Ward (05) B. p. 168, PI. XLiv. figs. 3, 4. 



3 Heer (77) ii. p. 65. « Cf. Pinus flexilis; 

 s Heer (82) ii. PI. vi. fig. 7. 



Bot. Mag. Tab. 8467. 



