■254 GINKGO. 



Gingko. There is a wide difference between the small entire 

 leaves home on fertile shoots and the larger ones with a shallow 

 central incision, and between these and the leaves of which 

 the lamina is divided into several comparatively narrow lobes 

 by divisions extending almost to the petiole. The leaves with 

 a large spreading and much dissected lamina are often found 

 on young and vigorous shoots or on seedlings ; these might well 

 be included in a distinct species if found as isolated fossils.' 



It has been customary to make use of Braun's generic name 

 Baiera'' or TJnger's term Jeanpaulia for leaves of a Giiikgo-Mke habit, 

 but having narrower or linear segments of the type represented 

 in PI. IX. Figs. 3-7. Such a generic distinction is no doubt, 

 in some cases at least, purely artificial, but as it serves a useful 

 purpose we may continue the custom, admitting that a distinctive 

 generic name does not necessarily imply a distinction of great 

 taxonomic importance. It is easy to obtain a series of fossil 

 leaves exhibiting various transitional stages between the type, 

 in which the lamina is entire, and such a form as that shown 

 in Fig. 6, PI. IX., where the lamina is reduced to forked acicular 

 segments. The limits of the two genera, Ginlcgo and Baiera, 

 cannot therefore be accurately defined, but, speaking generally, 

 the former name is applied to leaves with an entire lamina, or 

 with a lamina divided into two or more comparatively broad 

 segments, while the latter name implies leaves in which the 

 segments vary in breadth from less than 1 mm. to 2 or 3 mm. 

 in breadth, and may be usually described as Unear. 



1. Ginkgo digitata (Brongniart). 



[Hist. Teg. foBs. p. 219, pi. Ixi. bis, figs. 2 and 3, 1828.] 



(PI. IX. Figs. 1, 2, 9, and 10; Text-fig. 45.) 



1828. Cyelopteris digitata, Brongniart, Hist. veg. foss. p. 219, pi. Ixi. bis, 



figs. 2 and 3. 



1829. Sphenopteris latifolia, Phillips, Geol. Yorks. p. 148, pi. vii. fig. 18. 

 1833. Cyelopteris digitata, Lindley & Hutton, Foss. Flor. vol. i. pi. Ixiv. 



1 For figtires of several forms of leaves of the recent species, vide Seward & 

 ■Gowan (00), pi. a. figs. 62-66, 70. 

 ^ Braun (43), p. 20. 



