CALAMODENDRON. 



31 



medullary rays, but which Mr. Carruthers, with a})parcntly vciy good reasons, regards as 

 not having that character in S. vascularis. At the joints, where the branches spring from 

 the stem, the bundles of vessels there found much resemble those of /S. vascularis ; but 

 the tissue dividing the pseudo-vascnlar bundles in Calamodendroii is very different; and, 

 when seen in the small openings towards the outer part of the woody cylinder, has more 

 the appearance of a medullary bundle (being formed of cellular tissue) than those found 

 in Sifjillaria vascularis, which are liarred on all their sides, like the tubes forming the 

 woody cylinder of that plant. 



Although some years since it occurred to me, as well as to others, that small Cala- 

 modendron might possibly have been young Sigillaria, judging only from the rootlets 

 and some other portions of the plants, still we have seen that in the external characters of 

 the two genera there is no evidence to cstabhsli their identity. When also we come to 

 compare the internal structure of the tvvo plants, one differs from the other so much as to 

 dispose of any outward resemblance. In SifjiUaria, whether we take Dij)loxijlon cyca- 

 doideum or SigiUaria m!,'c?^/«;7>, there are two woody cylinders, formed of radiating tissues, 

 while in Calamodendroii there is only one such woody cylinder. The tubes composing 

 the internal radiating cylinders in the two first-named plants have their v/alls covered 

 with fine horizontal lines or stria3, either free or anastomising ; while in the last-named 

 plant the walls of the tubes arc much thicker, and are pierced by oval openings, having 

 their major axes at right angles to the direction of the tubes. In addition, the central axis 

 in Sigillaria has no horizontal diaphragms dividing it into separate portions, as is the case in 

 Calamodendroii, although the casts of the two central axes are each striated longitudinally. 



Prom the examination of the specimens described in this Monograph, Sigillaria and 

 Calamodendron must be considered as two distinct plants, although they doubtless 

 grew in similar positions, and in their habitats accompanied each other, in greater or 

 less abundance, during the whole of the time in which the Carboniferous strata were in 

 the course of formation, as is evident from the I'cmains of both plants being 

 so frequently found associated together in the " mother-coal" of this and other 

 countries. 



In the upper seam of coal in the section of the strata previously given (p. 12), and 

 there marked with a single asterisk, Calamodendron is by far the most conunon plant, and 

 Sigillaria (in the form of Biploxglon cycadoideum) is but rarely found ; while in the seams 

 marked with two and three asterisks, higher up in the series, Sigillaria vascularis is by 

 far the commonest form, and Calamodendron is rarely met with ; Calamodendron being 

 the smaller plant, forming the chief part of the small seam of coal, and Sigillaria the 

 larger plant, forming the greater proportion of the thicker seam of coal. Something 

 similar occurs in the Upper Coal-measures of Ardwick, whence the specimens Nos. 14 

 and 15 came. Calamites, then, is one of the most common plants met with, and it is found 

 associated with AsleropliylUtes, Lcjndodendron , Lepidoslrohiis, and Leindojjhjllum , but with 

 no traces of large-ribbed and furrowed Sigillaria, and only rare specimens of Sigillaria 



