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FOSSIL PLANTS. 



This specimen is instructive, since, though abundantly furnished with primary and 

 secondary medullary rays, or rather with the spaces which they occupied, all the cellular 

 tissues have disappeared from both, whilst the vascular foliar bundles are well preserved. 

 We are thus enabled to distinguish the respective areas occupied by the two tissues in a 

 manner that I have not succeeded in doing so distinctly in the other specimens described. 

 Each bundle is cylindrical, occupying the centre of the lenticular section of the ray, when 

 cut at right angles to its direction, and consisting of very small, barred vessels. Above 

 and below the vessels are open spaces ; but these were originally occupied by the cellular 

 tissues of the ray, the forms of the cells being strongly impresssed upon the indented 

 walls of the contiguous longitudinal vessels of the ligneous zone. I have not discovered 

 in this plant the cellular layer intervening between the medullary vascular cylinder and 

 the woody zone ; in this respect it appears to approach nearer to D. vasculare than to the 

 other forms. The vascular medullary cylinder or sheath is strangely marked ; but all the 

 medullary cellular tissues have disappeared. I pointed out some time ago 1 that some of 

 these Lepidodendra exhibited a feature not previously noticed ; namely, the vessels were not 

 only barred transversely, but, in addition, the transverse bars of lignine Avere connected by 

 a delicate series of threads of the same material, running parallel with the longer axis of 

 the vessel. I find this feature in all Diploxylons ; but in the Burntisland specimen it is 

 so faint that it can only be discovered under the microscope by a careful adjustment of 

 the light. The coarser transverse bars are also much more irregular in size, number, 

 and direction than is usual amongst the Diploxylons of the Upper Coal-measures. 



" The Di/ploxylon of Corda is so obviously identical generically with the Anabathra 

 of Witham that the latter name ought to be adopted in preference to the former one. 

 But ere long, in all probability, both these names will have to be abandoned, since there 

 appears little doubt that they represent the woody axes of some of the common 

 Lepidodendroid plants of the Coal-measures ; and, as soon as the identification of these 

 internal axes with their correlate external forms is indisputably accomplished, the yet 

 older names of the latter must become the adopted ones. Under these circumstances it is 

 scarcely desirable to disturb a widely accepted nomenclature, since any day may furnish 

 the required connecting link. 



" The general conclusion towards which all these additional observations point is the 

 same as that of the preceding memoir, which they strengthen and confirm, viz. that 

 all these varied plants are constructed upon a common type, and belong to one Lycopo- 

 diaceous family." 



31. Newberry 2 (Sigittaria) : — "Fossil-botanists have discussed the relations of 

 Sigittaria at considerable length, without reaching any universally accepted conclusion. 

 Professor Dawson considers they are Gymnosperms, while Mr. Carruthers regards them as 

 distinctly Cryptogamous, and more nearly allied to Lycopods than to the Conifers. My 



1 ' Monthly Microscopical Journal,' August 1st, 1809, pi. xx, fig. 10. 



2 " Report of the Geological Survey of Ohio," vol. i, Part II, 'Palaeontology,' p. B, 65, 1873. 



