DAW80X — 8I0ILLARIA, CALAMITE8, AMD CALAMODENDRON. 153 



inguish the structuros charactenstic of the subgenera of Si(jil- 

 ria, or absolutely to separate those from those of cerUiiu peculiar 

 •onifers on the one hand and from those of the higher acrogens on 

 the other. Young and succulent stems of Dado.n/lon may have 

 much resembled >SI(jillarla in their structure. Young stcnis of 

 Biy'dlaria proper may have approached closely to those of Favu- 

 Jaria ; and since I have shown* that the branches of Favularia 

 lesemblo Ckithraria in their scars, this last may have presented a 

 still feebler type of internal organization. Further, there is, as I 

 have already stated, reason to believe that some of the 8i)ecie8 

 referred by palueobotanists to the Clathrarla-diviBion are really 

 forms of LepklophhioH, These difficulties, in connexion with the 

 defective state of preservation of specimens, may excuse many diii'er- 

 encesof opinion, though 1 think the facts already stated in this paper 

 are sufficient to put all students of the subject on the right track in 

 regard to at least one leading type of theso plants, and to remove 

 some of the more fruitful sources of error. 



We may now proceed to incjuiro what light the structures of 

 SigiUaria throw on its affinities. On this (luestion, taken in its 

 most general aspect, there have, I believe, in modern times been 

 only two opinions, the views as to alliance with Euphovbim and 

 Cacti held by some older botanists having been given up. Some 

 botanists, conspicuous among whom is lirongniart, hold that Siyil- 

 larice were gymnospermous plants, allied to Cycadacea). Others are 

 disposed to regard them as acrogens, and as closely related to Lyco- 

 podiacea). 



In favour of the latter view may be urged the apparent associa- 

 tion with Sic/illaria of certain strobiles resembling those of Lepklo- 

 phloios, the points of resemblance between the tissues of Favularia 

 elegans and those of Lejndodendron, and the resemblance of certain 

 SnjillaricB, or supposed ISigillitrice, of the Clathraria-iy\}Q to Lepido- 

 phloios. 



In favour of the former view, wo may adduce the exogenous 

 structure of the stem of iSigiUaria, and the obvious affinity of its 

 tissues to those of Conifers and Cycuds, as well as the constant 

 association with trees of this genus of the evidently phanerogamous 

 fruits known as Triyonocarpum and Cardiocurpum. On the other 

 hand, the resemblance to Lepidodendron may be shown to depend 

 merely on comparisons of a part of the tissues of Sit/UIaria with 

 those of that genus. Grave doubts may also be entertained as to 

 whether strobiles of Lepidophloios, and even stems of that genus have 

 not been improperly mixed up with Sii/iUaria. 



It is probable that all botanists who have studied these plants, 

 might agree that, if not Gymnosperms, they at least present points 

 of affinity with them, and might bo regarded as in some sense a 

 link connecting them with Acrogens. Supposing this much to be 

 admitted, important questions remain as to their possible relations to 

 the modern Conifers and Cycads. The higher Sigillarue unquestion- 



* " Conditions of Deposition of Coal," Quart. Journ. Geol. Soc. vol. xiii. 

 ^ 130. 



