422 VEGETATION OF THE CARBONIFEROUS PERIOD 



those slender vessels from which the fascicles diverge and run to the 

 scars. In Sigittaria elegans, again., there are medullary rays; and 

 M. Brongniart states that the fascicles which run to the scars in that 

 plant originate in the inner zone of slender vascular tissue. I am how- 

 ever more inclined to suppose that they belong to a system of vessels 

 exterior to the main body of the woody tissue, for if they passed out by 

 the medullary rays they would be alternate with the latter, instead of 

 being placed immediately opposite to them. 



In Stigmarice the bundles of slender vessels are distinctly seen arising 

 from behind the woody zone and passing out by the medullary rays 

 to which they are opposite, not alternate, as in Sigittaria elegans. 



It is not by solitary characters, and least of all by such as the 

 arrangement of the tissues in the axis affords, that genera of plants are 

 referred to their natural orders. Amongst recent plants we see many 

 instances of plants indisputably belonging to one natural family having 

 the peculiar woody tissues of another and far distant group in the 

 system ; but these are mere analogical resemblances and by no means 

 indications of affinity. 



We may conclude then that the Sigittaria elegans was not far from 

 Lycopodiacea, and especially from Lepidodendron : — that it was of 

 much completer structure and higher organization than either is incon- 

 testable ; but the indications of a relationship with any individual group 

 higher in the series, or with Cycadece in particular, appear to me far too 

 feeble to justify our considering it as tending to unite these two natural 

 orders. It is a plant which (until we know its foliage or fructification) 

 must be considered as belonging to the great family of ferns (including 

 Lycopodiacea), displaying a relationship, though only of analogy, to 

 Cycadea in one point, and to Euphorbiacece and Cacti in others. 



Lepidodendron. — The anatomy of this genus has been well illus- 

 trated by Lindley and Hutton,* by Witham,f and more recently by 

 M. Brongniart, % whose analysis has left little to be desired regarding 

 the structure of its stem. Under the remarks upon Lepidostrobus which 

 follow this Essay will be found notices of a few remarkable points con- 

 nected with the occurrences of cylindrical specimens of the trunk of this 

 genus containing cones in their hollow axes ; and of the sculpture of 

 its surface as it appears before that compression to which the spe- 

 cimens are almost invariably subjected previous to or during their 

 petrifaction. 



Of the stems, branches, leaves, and fructification, we have thus a 

 very satisfactory knowledge ; but the nature of their roots is not ascer- 

 tained. Mr. Dawes, of West Bromwich, to whom I am indebted for 

 much information regarding the structural characters of coal-fossils, is 



* Lindley and. Hutton. f Witham. J Brongniart. 



