

DAWSON — SIOILLARIA, CALAMITE8, AND CALAMODENDRON. 151 



It has been held to bo an objection to the identification of tho 

 (Badgorous tissues above mentioned with those of ISir/illarin, that 

 the iStif/marlce, when their structure happens to bo preserved, show 

 merely scalariforra tissue. To this it may be answered : — (1.) That, 

 as Corda has shown*, some Stlf/muriie have reticulated or multi- 

 porous tissues. (2.) The tissue of lSti(jm<ina is not essentially dif- 

 ferent from tho 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. (IJ.) Many IS t it/ma ria; probably 

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

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

 of the stems of Sh/illafia proper. (4.) Inasmuch as the propor- 

 tions of pseudo-vascular and discigerous tissue may differ greatly 

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

 fhat the tissue, which is more particularly 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 tho 

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

 might be found to be more general than is commonly 8upi)osed. 

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

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

 perished. In my specimen of tho axis of SiijlUaria, 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 Si(jilluricn referred to in my previous 

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

 in proceeding from the circumference to the centre : — 



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

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

 thickened parenchymatous cells. 



{]>) 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-seoms. 



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

 with a single row of large bordered pores J, in the manner of Tines 



* Ileitriige zur Flora der Vorwelt. 



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

 roots of Lepidodendron. Baily seems to have .siiown that such roots belong to 

 the singular Lepidodendroid Cijclostigmi of the Devonian of Ireland; and 

 Schinipor asserts a connexion of Stigniaria roots with trees which he refers to 

 Knorria. 



t 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 unlincd portion of tho 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 Dadoxylon, 

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

 the tissues of the axis. 



