XL] BAIEEA 35 



more suitable name for certain forms of leaf is not governed by 

 any definite criterion: specimens described as Ginkgo sibirica, 

 G. lepida, G. concinna^, etc. are indistinguishable from leaves 

 referred by authors to Baiera. Similarly such a species as 

 B. Lindleyana differs very shghtly.from some forms usually in- 

 cluded in the genus Czekanowskia. Although leaves of Ginkgoites 

 and Baiera are abundantly represented in plant-bearing beds we 

 know very httle of the habit of the f ohage-shoots ; in a few cases 

 there is evidence of the occurrence of several leaves on a single 

 short shoot (fig. 646) ; in Baiera paucifartita, for example^, the 

 habit is the same as that of Czekanowskia and Phoenicopsis, but 

 in view of the frequent preservation of Czekanowskia leaves still 

 attached to an axis it is surprising that the leaves of Baiera almost 

 always occur as detached specimens. The explanation may be 

 that in Ginkgoites and Baiera the fohage-leaves were borne on 

 long and dwarf-shoots as in the recent species Ginkgo hiloba, 

 whereas in Czekanowskia the leaves were confined to shoots of 

 limited growth as in Pinus. Some specimens described by Salfeld* 

 from the Solenhofen beds of Bavaria as Baieral longifolia Heer 

 are interesting in this connexion; they consist of fairly stout 

 branches bearing alternate leaf-hke organs having the habit of 

 Baiera longifolia but subtended by a short and thick recurved 

 spinous process. There is no means of deciding from the avail- 

 able material whether the resemblance of the leaves to those of 

 Baiera is an expression of relationship or merely a case of parallel 

 development, nor have we any means of determining the morpho- 

 logy of the leaves and the subtending spines. The Solenhofen 

 plant agrees in habit with Sewardia latifolia* from the Wealden 

 of England and is included under that genus. While relationship 

 between Sewardia and Baiera is by no means excluded, it is clear 

 that the species of the former genus differ considerably from 

 typical representatives of Baiera and Ginkgoites. Certain species 

 of Baiera exceed in size the leaves of any example of Ginkgoites, 

 notably B. Simmondsi, B. spectabilis, and others. 



The specimens described by Fontaine and Berry from the 



1 Heer (77) ii. PI. xni. figs. 6—8. 



2 Nathorst (78^) B. PI. xxi. 



3 Salfeld (07) B. p. 195, PI. xx. fig. 3; PI. xxi. fig. 1. 

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