3 1 6 Kisch. — The Physiological Anatomy of 
As far as the present investigation goes, none of the petrifactions 
examined show any sign of longitudinal fissures, except one obviously 
much mutilated specimen of Lepidodendron brevifolium . The oldest 
example of Lepidodendron selaginoides has a periderm two inches thick, 
which is divided into wedges, as is usual in this species, but the wedges 
taper inwards towards the centre of the stem ; while there are specimens of 
Lepidodendroji Wunschiannm and of Stigmariae with still thicker periderm 
and no sign of furrows. Again, impressions of great size are found with the 
Text-fig. 26. Lepidodendron fuliginosum. Dia- 
grammatic transverse section of a specimen showing 
several narrow bands of periderm. The periderm, pd, is 
shown in black ; st } stele. Will. Coll., 385. x 2. 
Text-fig. 27. Lepidodendronfnli- 
ginosum. Transverse section in the 
periderm showing layers added by 
division of the cells on the inner 
margin. U. C.L. Coll., A 32. x 90. 
leaf-bases still intact and showing no Assuring or distortion, as, for example, 
a specimen attributed to L. aculeatum in the Natural History Museum, with 
leaf-cushions over two inches long. 
There is another difficulty with regard to the exfoliation theory which 
was touched on by Williamson in his monograph on Stigmarial In Lepido- 
dendron selaginoides ( vasculare ), for instance, Hovelacque considered the 
periderm as true cork, but it is now generally recognized that the bulk of 
the secondary cortical tissue is phelloderm. If £ at a later stage the cushions 
1 Williamson ( 43 ), p. 21. 
