DAAVSOIs^ — SIGILIAKIA, CAIAM.ITES, AND CALAM0DI2a)E0K. 149 



The exception above referred to is, that in one tree, which from 

 its markings I supposed to be a SigiUaria, tlie woody tissue was com- 

 posed of large cells, with many rows of pores (" multiporous tissue " 

 of my former papers) of the type of that to which Prof. Williamson 

 has given the name of Dictyoxylon''^. Since, however, as Prof. Wil- 

 liamson has well shown, such tissue may be regarded as a modifica- 

 tion of the discigerous variety, and since Corda long ago found it in 

 the axis of a species of Stigmariaf, there is nothing improbable in the 

 supposition that we have here merely an indication of a specific or 

 subgeneric difference coming within the Hmits of the genus SigiUaria, 

 as at present understood. 



It is to be observed that most of the erect trunks in the coal-for- 

 mation have not preserved their external markings with sufficient 

 distinctness to allow the species to be determined by the leaf-scars ; 

 but they show in most cases the characteristic ribs and rows of 

 punctures or areoles, modified in the manner which is usual in the 

 case of old trunks of these plants near their bases J. 



In Plate YIII. figs. 12, 14, 15, 16, 1 have represented some of the 

 more usual forms of tissue in the erect SicjiJlarice. 



In Plate X. I have represented the best-preserved axis in my 

 possession. Pig. 23 shows the structures in the entire stem, except 

 the portions of cellular bark lost by decaj'. In the centre is a Stern- 

 hergia-^ith. («). This is surrounded by a woody cylinder (6), the 

 inner part of which (fig. 24, hi) consists of scalariform tissue pass- 

 ing towards the outer surface into pseudo-scalariform (h 2), reticu- 

 lated with pores {h 3), and discigerous (h 4). This woody axis has 

 medullary rays (figs. 25, 2Q, 27), and is traversed by bundles of 

 scalariform tissue proceeding from the inner part of the cylinder. 

 The outer portion of the inner bark, not seen in this specimen, but in 

 similar prostrate stems, is composed of elongated thin-walled bast- 

 cells, with somewhat obtuse ends, and of larger diameter than the 

 woody fibres of the axis (fig. 29). The tissues of the woody axis 

 are all arranged in radial series (fig. 28). 



Prostrate Trunlcs. — In the coarse shaly coals, and in the roof- 

 shales of the ordinary seams, there are often flattened stems of 

 SigiUaria, having the tissues partially infiltrated with carbonate of 

 lime or carbonate and sulphate of iron. The tissues usually pre- 

 served in these flattened trunks are those of the bark, and more 

 especially its large bundles of elongated or prosenchymatous cells 

 (" bast-tissue "). Of this I have been enabled to obtain very perfect 

 specimens from these flattened trunks. In a few instances only tlie 

 woody structure of the axis remains, showing the same descriptions 

 of wood-cells already referred to as characteristic of the erect trees. 

 Plate YIII. fig. 11 is an example of the structures in one of these 

 prostrate stems. 



* Trans. Eoyal Micro. Soc, Aug. 1869. 



t Beitrage zur Flora &c. 1845, pi. siii. Corcla regards this as the structure 

 of 8. ficoides, and the more ordinary variety as that of 8. anabathra. 



I The species which I have described as 8. Brmunii, Acad. Geol. 2nd edition, 

 may be regarded as a representative of these trees. 



