DAAVSOK — SIGILLAEIAj CALAMIXES, AND CALA-MODENDEOBT. 151 



It has been held to be au objection to the identification of the 

 discigerous tissues above mentioned with those of Sigillaria, that 

 the Stigmarice, when their structure happens to be preserved, show 

 merely scalariform tissue. To this it maybe answered : — (1.) That, 

 as Corda has shown*, some Stiginarice have reticulated or multi- 

 porous tissues. (2.) The tissue of Stigmana is not essentially dif- 

 ferent from the pseudo-scalariform fibres of the stem, and is arranged 

 in a similar manner, showing that it is homologous rather with 

 woody than with vascular tissue. (3.) Many Stigmarice probably 

 belong to Favularia and similar forms, or possibly even to Lepido- 

 dendroid plants t. In either case the structure would be unlike that 

 of the stems of Slgillaria proper. (4.) Inasmuch as the propor- 

 tions of pseudo-vascular and discigerous tissue may differ greatly 

 in the stems of Sigillance, it would not be unreasonable to suppose 

 that the tissue, which is more j)articularly important for the 

 strengthening of the stem, should be absent, or in a feeble state of 

 development, in the root. Something of this kind occurs in the 

 roots of Cycads, and perhaps, if detailed examinations were made, 

 might be found to be more general than is commonly supposed. 

 (5.) The outer part of the axis, being left exposed by the decay of 

 the loose cellular matter of the iuner bark, may, in most cases, have 

 perished. In my specimen of the axis of Slglllaria, above described, 

 it is in parts much disorganized, and has disappeared, or been con- 

 verted into coal, on one side. 



The evidence included under the above heads is sufficient to show 

 that the ordinary ribbed Sigillarice referred to in my previous 

 papers, possessed in their main trunks the following kinds of tissue, 

 in proceeding from the circumference to the centre : — 



(a) A dense cellular outer bark, usually in the state of compact 

 coal — but when its structure is preserved, showing a tissue of 

 thickened parenchymatous cells. 



(6) A very thick inner bark, which has usually in great part 

 perished, or been converted into coal, but which, in old trunks, 

 contained a large quantity of prosenchymatous tissue, very tough 

 and of great durability. This "bast-tissue" is comparable with 

 that of the inner bark of modern Conifers, and constitutes much of 

 the mineral charcoal of the coal-seams, 



(c) An outer ligneous cylinder, composed of wood-cells, either 

 with a single row of large bordered pores %, in the manner of Pines 



* Eeitriige zur Flora der Vorwelfc. * 



t Brown, in 1847, described, in the ' Proceedings ' of this Society, Stigmaria- 

 roots of Lepidodcndron. Baily seems to have shown that such roots belong to 

 the singular Lepidodendroid Ci/clostignia of the Devonian of Ireland; and 

 Schimper asserts a connexion of Stigmaria roots with trees which he refers to 

 Knorria. 



X These are the same with the wood-cells elsewhere called discigerous tissue, 

 and to which I have applied the terms uniporous and multiporous. The mark- 

 ings on the walls are caused by an unlined portion of the cell-wall placed in a 

 disk or depression, and this often surrounded by an hexagonal rim of thickened 

 wall ; but in all cases these structures are less pronounced than in Badoxylon, 

 and less regular in the walls of the same cell, as well as in different layers of 

 the tissues of the axis. 



