350 SPHENOPHYLLEAE. 



therefore consider it to be a transverse section of a root, but to what plant 

 it belongs is quite uncertain. In the nodes the secondary growth is 

 traversed by the leaf-trace-strands, and near each of these is an interspace 

 of tubular form filled with a delicate parenchyma. 



In some particularly well-preserved specimens Renault l has observed 

 the bast in the form of a thin-walled crushed tissue surrounding the 

 secondary wood. Single larger lumina in it he considers to be sieve- 

 tubes. Immediately outside the bast is a layer of tissue, which he 2 terms a 

 'suberous layer corresponding to the protecting sheath of the mass of phloem 

 and xylem,' and which he derives from the tangential division of the cells of 

 the protecting sheath. This tissue, with its patelliform or tubular cells in 

 radial rows as given in Renault's figure '\ looks in fact very like a periderm, 

 and may be a periderm, if Renault's further statements, which I cannot 

 judge of from the material in my possession, are ultimately confirmed. He 

 says in effect that in the old piece of stem mentioned above with fifteen layers 

 of secondary wood and with the rind removed, there are several of these 

 'couches sube'reuses' present, separated from each other by layers of crushed 

 bast (' tissu corne'). This, as he distinctly says 4 , would mean normal forma- 

 tion of bark. The accompanying figure would rather lead us to regard these 

 layers of ' tissu corne' to be simply layers of sclerenchyma, such as so often 

 alternate in the phellem with the cork-cells. In that case we must regard 

 the whole not as rhytidom, but as one connected mass of periderm. 



The pieces of stem which come under notice are usually short frag- 

 ments without their leaves, and commonly even without their rind. Renault 

 however has in two cases succeeded in finding specimens which showed the 

 leaves in situ and with their structure preserved. Williamson 5 also deals 

 with a similar case. Here the stem was imbedded in the stone, and only 

 the longitudinal and the transverse sections could be observed, not the form 

 of the lamina of the leaf. Fig. 48, 2 reproduces the drawing in Renault 

 which gives the clearest view of a specimen of the kind. It shows the stem 

 surrounded by six four-nerved leaves. Renault has also given two trans- 

 verse sections of another species, his Sphenophyllum Stephanense, taken 

 from a stem at different heights. Only two leaves are distinctly preserved ; 

 those in the lower section are three-nerved, in the upper section they are 

 replaced by six small one-nerved transverse sections swollen in the middle, 

 and answering to the three teeth into which each leaf has meanwhile divided. 

 Here too from the position of the leaves there would not have been more 

 than six present. In Williamson's specimen just alluded to the arrange- 

 ment of the leaves is less clear, because only radial and tangential sections 



1 Renault (2), vol. iv, Introd. t. A, f. 3 c. * Renault (2), vol. iv, Introd. p. 4. 3 Renault (2), 

 vol. iv, Introd. t. D, ff. 3, 4. * Renault (2\ vol. iv, Introd. p. 13 ; t. D, f. 4. s Williamson 



(1), V, t. 3. fl Renault (16), t. 4, ff. 5, 6. 



