LEPIDODENDREAE. 



225 



English material than two preparations of Witham's Anabathra in a very 

 bad state of preparation, since he writes as follows 1 : ' The fact observed 

 by Williamson of young branches of Sigillaria vascularis, without exterior 

 centrifugal wood, forming a continuous zone round the centripetal cylinder 

 is certainly correct, but we do not doubt that the foliar bundles given off 

 from it are formed, like those of Diploxylon and of the Sigillariae, of two 

 distinct portions with their growth inverse in relation to one another.' 



The above arguments have only gained in strength from Zeiller's 2 

 discovery, which has proved that an archegoniate fructification resembling 

 Lepidostrobus is beyond doubt a Sigillaria, on which subject some further 

 remarks will appear below. For now that we know that the Sigillariae 

 also belong to this class, the argumentation of Renault and his predecessors 

 has entirely lost its point of departure. I cannot be wrong in this per- 

 suasion, when he himself has recently 

 attempted to save his case by the 

 following assumption. He says 3 : ' The 

 Sigillariae, an essentially transitional 

 group, would thus be divided into 

 Leiodermarieae or phanerogamous 

 Sigillariae with smooth rind allied to 

 Cycadeae and Rhytidolepis or crypto- 

 gamous Sigillariae with fluted rind 

 near to Isoetes.' 



The behaviour of the central 

 strand in the bifurcation of the stem 

 as represented by Williamson 4 and 

 Binney 5 is peculiar (Fig. 24). It ap- 

 parently divides at that point into two 

 halves. The peripheral exclusively 

 tracheal portion separates into two semicircular segments, and each segment 

 incloses a half of the middle mixed tissue which is in immediate connection 

 with .the surrounding parenchyma on the side towards the centre of the 

 stem. Then each of the semicircular tracheal outer portions, gradually 

 closing in each branch round the central tissue, unites into a circle and 

 the normal structure is restore?!. Corda's 6 Leptoxylon geminum must 

 quite certainly be considered to be such a Lepidodendron-stem in the act 

 of bifurcation, though owing to its unfavourable state of preservation it 

 is not clear whether it belongs to this type or to that of Lepidodendron 

 Harcourtii, With, which we are about to consider. 



Unlike the vasculare-type, within which we are not in a position to 



FIG. 24. Transverse section ot one ot the central 

 bundles of Lepidodendron selaginoides, Will_.imme- 

 diately above the bifurcation. On one side, the inner 

 side, the bundle is not closed up again, its central tissue 

 abuts immediately on that of the rind. After Binney. 



1 Renault (2), vol. i, p. 150. 2 Zeiller (12). 3 Renault (9). 



t. 49, f. 8. 5 Binney (1), in, t. 14, ff. 4, 5. 6 Corda (1), t. 15. 



Williamson (1), XI, 



