36 GINKGOALES 



[CH. 



Potomac group iu Virginia as Baiera foliosa\ consisting of an axis 

 bearing crowded leaves with a deeply and rather irregularly divided 

 lamina and a comparatively broad and flat basal region, are not 

 typical examples of the genus but agree more closely in habit 

 with the older genus Dicranophyllum : their precise position 

 cannot be definitely determined. 



The structure of the cuticles is known in a few species from 

 accounts pubUshed by Schenk^, Nathorst* and Thomas*; the 

 epidermal cells are sometimes characterised by fairly prominent 

 papillae on the outer walls (fig. 647) and the stomata, more 

 abundant on the lower surface but present also on the upper 

 surface, closely resemble those of Ginkgo and Ginkgoites; the 

 guard-cells are shghtly depressed and are surrounded by 5 — 6 sub- 

 sidiary cells with strongly cuticularised and projecting walls 

 (fig. 647). Nathorst* has drawn attention to the presence in 

 B. spectabilis of traces of some secreted substance in the mesophyll 

 recalhng the secretory tracts in the leaves of Ginkgo. 



Braun and other authors have included Baiera in the Fihcales, 

 and attention has been called to the danger of confusing true 

 Fern-fronds with leaves of Baiera. Berry's discovery of sporangia 

 on the hnear segments of Baiera-]ike leaves from the Potomac 

 beds, originally referred by Fontaine to his genus Baieropsis and 

 regarded by him as Ginkgoaceous, illustrates the possibihties of 

 error in determinations founded on leaves alone. The fertile 

 examples of Baieropsis have been made the type of a new genus 

 Scliizaeopsis^, other species of Fontaine's genus being transferred 

 to the genus Acrostichopteris ; they differ from Baiera in their 

 attachment to slender axes and are no doubt portions of compound 

 Fern-fronds. It is impossible to define with confidence the precise 

 geological range of the genus; leaves from Permian and Upper 

 Carboniferous strata agreeing with Baiera in the deep dissection 

 of the lamina have been assigned to the genus Ginkgophyllum 

 {PsygmophyUum) and compared with Saporta's Ginkgophyllum 

 Grasserti (fig. 669, p. 87). In imperfect specimens it is not always 

 possible to draw a sharp fine between Baiera and species of Psygmo- 



1 Fontaine (89) B. p. 213, PI. xciv.fig. 13; Berry (11) p. 372, PI. lix. 

 '- Schenk (67) A. PI. vi. figs. 1, 2; PI. ix. figs. 11—13. 

 ' Nathorst (06). i Thomas (13=) p. 244, fig. 5. 



' Nathorst (06) p. 9, fig. 9. e Berry (11) p. 214; (IP). 



