30 FOSSIL PLANTS. 



IV. Concluding Remarks. 



After the description of the specimens of Calamodendron in this Monograph, it will not 

 be out of place to notice the points in wdiich this genus of plants differs from Sicjillaria, 

 especially from the plant which I have described as Sigillaria vascularis} 



The form of the roots of Si(^iUarin varies from that of Calamodendron. It is true that 

 the termination of Stigmaria is club-shaped, like that of Calamodendron, and the rootlets 

 are arranged in quincuncial order, as Avas shown in the paper of mine previously alluded 

 to (see above, p. 15) ; but in the latter plant we find no trace of the regular bifurcation 

 of the main and lesser roots ; and the roots appear to have been small in size, with regard 

 to the stem and branches of the plant, when compared with similar parts in Slgillaria. 

 From all the evidence which has been obtained by me, Calamodendron must have been 

 a plant of small size when compared with Sigillaria. 



The largest Calamodendron that has come under my notice is one from the Middle 

 Coal-measures, and was found by the late Mr. John Atkinson, F.G.S., in the neighbourhood 

 of Chesterfield ; it is now in my possession. The cast of the central axis of this specimen 

 is five and a half inches in diameter ; and, taking the proportions of smaller speci- 

 mens, the woody cylinder, exclusive of the bark, would probably be about one foot in 

 diameter; a small size, when compared with some stems of Sigillaria, which have been 

 found to measure seven feet in diameter at the base. 



The terminal branches of Calamodendron were also of small size, some of them not 

 being more than xsoths of an inch in diameter ; whereas the smallest specimens of Sigillaria 

 vascularis, which have come under my notice have been about half an inch across ; and 

 the branches, like the roots before mentioned, in Calamodendron have none of the dicho- 

 tomous characters so distinctly shown in Sigillaria vascularis. 



The organs of fructification did not reach more than one third of an inch in length, 

 and were of a diminutive size even when compared with the small bulk of the plant. We 

 cannot well compare them with similar parts of Sigillarla, as at present we are unable to 

 speak with absolute certainty as to the fructification of that plant, which was most pro- 

 bably a cone nmch larger than that of Calamodendron. Indeed the small size of the 

 organs of fructification in Calamodendron is one of the most singular characters of the 

 plant. 



There is a difference also observed in the bundles of vessels passing from the centre 

 to the circumference, dividing the wedge-shaped masses of pseudo-vascular tissue, and 

 which M. Adolphe Brongniart and some other authors considered to be of the nature of 



1 'Quart. Journ. Geol. Soc.,' vol. xviii, p. lOG, pi. IV and V. 



