B34 Reviews — Dawson's Acadian Geology, 



stems themselves, which could without doubt be referred by their 

 external characters to a particular genus. 



The beautiful specimens of Calamites nodosus, Schloth., figured by 

 Lindley and Hutton, belonged to a repeatedly branching plant, and 

 were not simple plants as represented at C, Fig. 2 ; an examination of 

 the original specimens now deposited in the Newcastle Museum 

 shows that the form to which they gave this name are really the 

 branched fruiting spikes, and not the true foliage of Calamites. 



Our own observations in regard to the structure of these plants 

 differ so much from those of Dr. Dawson that we are compelled to 

 modifj'- somewhat the systematic position he gives to Sigillaria as 

 well as to Calamodendron. It is remarkable that so little is known 

 of a genus of plants which are so abundant in Carboniferous strata, 

 and the more so that every particular is known regarding the struc- 

 ture of its associated genus Lepidodendron. Dr. Dawson has ample 

 authority for his restoration of his L. corrugatum (Fig. 3) as far as it 

 goes. The sporangium may have been of a different form, and only 

 one connected with each scale, as in Lepidostrohus ; but otherwise 

 there can be no hesitation in co-relating all the other parts. The 

 author has done good work in tracing the different forms of scars, 

 which without jDersevering research would have been, by a more 

 hasty and careless worker, referred to several distinct species. That 

 Lepidodendron belongs to the vascular cryptogams, and had the habit 

 of, if it did not belong to the Order of Lycopodiacece every one 

 acknowledges. And that in all characters in which they can be 

 compared — except the microscopic structure of the vascular axis of 

 the stem — these two genera were closely allied is also generally 

 admitted — indeed it is very difficult in many cases to determine to 

 which of the genera some species should be referred, and no 

 characters can be drawn which will suffice to distinguish the Favu- 

 laria group of Sigillaria from the group of Lepidodendron to which 

 Dr. Dawson applies the name Lepidophloios. 



The characters derived from the internal structure of the stem are 

 those upon which the two groups are separated into genera, and by 

 some authors placed widely apart systematically. Brongniart's 

 admirable memoir on the structure of Sigillaria elegans is still the 

 most complete exposition of the subject. He describes it as consist- 

 ing of a cellular axis surrounded by a double cylinder of vascular 

 tissue, the inner consisting of distinct bundles of a lunate form and 

 the outer regularly arranged in radiating series, sometimes broken 

 up by narrow radiating intervals supposed to have been occupied by 

 medullary rays. Beyond the vascular cylinder was a cellular laj^er, 

 becoming more dense towards the circumference, and traversed by 

 the vascular bundles which passed out to the leaves. This descrip- 

 tion agrees with the figure given by Dr. Dawson (Fig. 4, C), except 

 that Brongniart saw no indication of diaphragms (a) in the cellular 

 axis, or of a cylinder of disc-bearing tissue (b) ; and also with the 

 section of {Lepidodendron) Lepidophloios Acadianvs (Acadian Geology, 

 p. 457, fig. I). ^ 



Dr. Hooker, in his Essay on the Carboniferous Flora, doubts 



