Johnson — O71 Bothrodendron (^Cyclostignia) kiltorkense. 515 



Potouie (Die Silur- Flora) gives a detailed and well-illustrated account of 

 Dechenia Roemeviana, and concludes (I tliink justifiably) that Deehenia is a 

 Stigmaria and the underground organ of Cyclostigma hercijniuni. His figures 

 show the Knorria-stage of the leaf- scars, attributed to Bothrodendron or 

 Cyclostigma, and in the same petrification the characteristic scars of the 

 Stigmaria appendages. Perfect proof of the correctness of his view would be 

 furnished if the Dechenia showed the surface-markings and loaf-scars of 

 Bothrodendron. As at present known tlie Knorria-stage may, as Nathorst 

 says, equally well belong to anotlier Lepidophyte. Nathorst cannot accept 

 Potonie's identification of Dechenia with its Stigmaria features as part of 

 Bothrodendron, but sees in a forking specimen he himself figures (op. cit., 

 Tf. 10, figs. 4 and 5) the probable rhizome of Bothrodendron. His figures 

 show a bifurcated axis covered with leaf-scars which occur on cushions 

 slightly raised and directed towards the free ends of the arms. Further, the 

 surface of the whole axis, it is noted, is marked by a slight longitudinal 

 striation. I can see nothing special in the specimen as illustrated to 

 support the view that it is the rhizome of Bothrodendron. Nathorst thinks 

 that Stigmaria is itself so peculiar, if not enigmatical, a morphological organ, 

 that variation in Bothrodendron from the normal seen in other Lepidophytes 

 need not surprise one. Nathorst states that if the forked axis lie figures is 

 not rhizomatous, then the majority of the stems figured in various publications 

 are drawn upside down. It is curious to note that Nathorst himself seems to 

 make this possible eiTor. His illustration — Tf. 14, fig. 5 — shows a small 

 piece of stem in which the leaf-scars are identical in character with those 

 on the unforked part of his rhizomatus axis, in Tf. 10, fig. 4. My opinion is 

 that the former shows the leaf-scars in the right position, and that his 

 supposed rhizome is simply part of an ordinary aerial dichotomizing 

 shoot. Nathorst's illustrations of B. h'Uorkense are the most ample and 

 satisfactory hitherto published, but in the lithographic ones the leaf-scar 

 illustrations leave something to be desired in definiteness. My own expe- 

 rience, based on the examination of leaf-bearing and other shoots, is that 

 the leaf-scar, when on a leaf-cushion or not, is limited on its lower side 

 by a more or less well-defined rim or ridge which is continued upwards 

 to complete a round or somewhat oval border beyond which it runs out into 

 a sloping surface (Plate XXXVII, fig. 4). The ligular scars, if admitted as 

 such, may occur where this inclined surface joins the leaf-scar proper, so that 

 the incline may be included as part of the leaf-field or (when projecting) leaf- 

 cushion. In some cases where the impression or cast is not the outer 

 carbonaceous surface of the shoot, but the shoot surface as seen from within, 

 or even its counterpart, impress or " mould," on the stone, tlie leaf-scar 



SCIENT. PKOC. K.D.S., VOL. XIII., NO. XXXIV. 4 G 



