Johnson — On Bothrodendron {Cyclostigma) Idltorkense. 509 



ridge suggestive of a central vascular axis in the living stem. (One would 

 naturally assume from comparison with other Lepidophytes that tlie stem of 

 B. kiUorJieiise would possess a central vascular axis — a protostele at least. 

 Rhode and Haughton speak of sucli an axis, and roughly indicate it in their 

 drawings. In several pieces of stems the broken end shows traces of 

 carbonized remains in the hollow cylinder, though in one of the best-preserved 

 pieces (Plate XLI, fig. 2) there is no sign of such an axial strand. The stem 

 appears in this section as hollow as an internode of Equisetum. The fact 

 that the Bothrodendron stems are found nearly always in a flattened state 

 (sometimes like sheets of paper) lends support to the view that the stem was 

 liollow or occupied by soft perishable tissue. It is possible that the specimen 

 (Plate XXXY, fig. 3) illustrates a difference of illumination of the two sides 

 of the stem. The photograph shows clearly that the difference occurs, whatever 

 the physiological cause may be. This specimen should be compared with the 

 older one (Plate XXXV, fig. 2), which shows closely approximated leaf-scars 

 in the upper part and separating ones in the lower thicker part of the stem- 

 impressiou — a clear illustration of the increasing distance between the scars, 

 which accompanies and is caused by the extension of the surface as the 

 stem enlai'ges. It was failure to recognize tlie ribbed stem as found in 

 Bothrodendron which led Heer to place such specimens in his Calamites 

 radiatus, now known &s Asterocalamites scrobiculattcs, siud in part as Pseudobornia 

 ursina, Nath. Potouie devotes some attention to the description and explana- 

 tion of calamitoid characters in his Cyclodigma hercyniiim. These characters 

 are very like those in Boihrodendron kil(orkeuse,hat by no means so pronounced ; 

 and Potonie expressly mentious, apparently to avoid the possibility of con- 

 fusion with the Equisetacese, that naturally in it horizontal zonation does not 

 occur. The photographs show that it does occur in B. kiltorkense. The figures 

 give a good idea of the general character of the ribbed features, and show, too, 

 that Potonie's explanation is not sufficient to account for the appearance. 

 Plate XXXVIII, fig. 2, shows that the ribbed feature is not confined to tlie 

 Knorria-stage, as Potonie supposes, but is clearly marked in stems with cortex 

 and epidermis preserved. In the specimen the finer sculpturing of tiie stem 

 is evident, and the leaf-scars showing the typical condition with three sears 

 are readily observable. Potonie states — and I agree with him — that in the 

 Knorria-stage the petrified parichuos-strand of the leaf rests in contact with 

 that of the leaf immediately above or below it, and that thus more or less 

 straight ridges arise. The strand in some cases is not equally prominent 

 throughout its length, and in consequence the ribs, though straight, may 

 not be so regular or continuous as those of a Calamite, especially of an 

 Asterocalamite, in which the vertical ridges coincide from internode to 



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