[From the Qfarterly Journal of the Grolooical Society for 



May 1871.] 



On the Structurr and Affinities of Sioillakia, Calamitrs and 

 C'alamodendkon. By J. \V. Dawson, LL.D., F.U.S., F.G.S,, 

 Principal of M^Oill Univeryity. 



(Read May 11, 1870 ».) 

 [Plates VII -X.] 

 1. SiGILLAUIA. 



The difficulty of arriving at a coiTcct knowledge of tlie structure 

 of those curious trees is caused principally by the unecjual durability 

 of the different piirts of the stem. It arises from this that some 

 portions liavc usually perished, while others were in process of 

 mineral iz'ition, and the portions which remain have in a great 

 degree lost their original form and arrangement. The outer bark, 

 while extremely durable, was too impenetrable to be jjreserved in 

 any other way than as compact coal. The fibres of the bark and 

 of the woody axis are often mineralized or imperfectly preserved as 

 mineral charcoal. • The cellular poiiions of the bark and of the axis 

 have usually entirely disappeared. Still, im[)erfectly preserved stems 

 can be obtained in great abundance in any coal-field by those who 

 are content to work on such unpromising material. 



Probably the finest specimen of a t^hjillaria hitherto described is 

 tliat of S. ehf/ans, so admirably figured by IJrongniart, and which 

 has long served to give to the student of pala>ol)otany his ideas of 

 the structure of the genus. Unfortunately, however, Brongniart's 

 specimen represents a small or young stem belonging to the some- 

 what aberrant subgenus FaruJuria ; so that it fails to give an adequate 

 idi'a of the structure of the typical fossil Sii/Ulariir, which aro 

 much more common and important, at least in the coal-fields of 

 Nova Scotia. The structure of these last, as observed in specimens 

 obtained at the South Joggins, was, I believe, first descrilied by mo 

 in my paper on the Vegetable Structures in Coal, published in the 

 'Journal' of this Society in 1855K The specimens subsequently 

 figured in the ' Journal ' of this Society, and in the ' Transactions ' 

 of the lloyal Society, by Mr, Binney, under the name of /S, vascida7-is, 

 belong, in ])art at least, to types of structure (]uite distinct from that 

 of the ti'ue Sl(/dlaninf. 



My own results as to the typical Sn/iUariff are thus shortly 

 summed up in my ])aper on the " Conditions of DcjKtsition of 

 Coal" J : — "In the restricted genus Siijilhtriu the ribs are stmngly 

 developed, except at the base of the stem ; they are usually nnich 



* For the discussion on this paper see Quart, Journ, Gaol. Soc. vol. xxvi. 

 p. 4'.)(). 



t It would seem that the speciniens figured by Mr. Binnoy us SicjiUuria 

 vascularis (Philos. Traiis. vol. civ.) belong in part to the axia of a remarkable 

 Sigillarioid tree, of which specimens have been kindly shown to nu; hy Prof, 

 Williamson, and in part (especially pi. xxxv. fig.-'. .^ & (i) to the vholc .stnn 

 of a Lej>i(/o(fn/c/ro7i. The latter plant has been desi'ribed hy Mr. C'arruthers (i.s 

 L('pit(oihndro)i srl/if/inniflfs. 



J Qnnrt. Journ. (ieul. >;oi'. vol. xxii. ]>. l'-".'. 



