276 Contributions towards Establishing the General Character 



in consequence of the junction of the threads of cuticle with the leaf- 

 bases, the ribs (1, 2, and 3) have been increased in width, — a circumstance 

 which throws the leaf-scars ax, ax over to the left side. An exami- 

 nation of the figure of Sigillaria brings to view the same character, that 

 is, the leaf-scars, instead of running up the median line of the ribs, are 

 placed on the left side. This does not appear to prevail to any extent : 

 nevertheless, I have observed it on other specimens, and Mr Hutton 

 possesses one which shews it very decidedly. Between this last and 

 Ahies Webbiana, the similarity in this respect is such, as to prevent the 

 adoption of any other conclusion than that which refers this character 

 on both plants to one and the same cause. 



It has already been remarked, that I have not succeeded in tracing 

 any threads of cuticle on Sigillaria. It is necessary to mention, how- 

 ever, that, on the specimen which is figured, there are appearances of 

 commissural lines between some of the leaf-scars and the immediate 

 superimposed leaf-bases ; these are represented running obliquely from 

 the apex of some of the leaf-scars into the furrows on the left. Whether 

 these lines are such as they appear, I am not prepared to answer in the 

 aflirmative. Their direction and position are certainly very much in fa- 

 vour of this being the case, as will be seen by referring to the restoration 

 (in dotted lines) which has been attempted of the leaf-bases and threads 

 of cuticle : the latter, it will be perceived, conform completely with the 

 direction and position of the supposed commissural lines. If we com- 

 pare the leaf-bases and threads of cuticle thus restored with the corres- 

 ponding parts of Abies Webbiana, their resemblance to each other will 

 appear exceedingly striking. 



Thus the circumstances just mentioned connected with Sigillaria, go 

 far towards shewing that its leaves are resolvable into spirals, which 

 agree with those of Coniferce and Lepidodendra. Associating this with 

 the way in which it has been shewn that the rude ribs of some Conifers 

 have been formed, we are necessarily led to conclude that the same but 



more regular character of Sigillaria has been similarly produced, the 



difierence as regards the latter parts in the fossil being due to the com- 

 plete confluence of all the leaf-bases and other parts which belong to a 

 rib, or, the contrary, as generally obtains in Coniferce* But, lest it 

 should be maintained that the absence of threads of cuticle on Sigillaria 

 and the rare occurrence of these parts uniting with the leaf-bases on re- 

 cent Conifer(B, render this conclusion inadmissible as far as the former 

 plant is concerned ; it may be stated that the solitary case which has 

 been cited, of threads of cuticle occurring on Lepidodendron, opposed as 

 it is by hundreds of specimens in which nothing of the kind is to be found 

 nevertheless proves that the threads of cuticle have all but universally 



* The remarkable perpendicularity of the ribs of Sigillaria, according to this 

 view, will have resulted from the leaves of one spiral being completely superim- 

 posfcd to those of the spiral which coils immediately beneath. 



