THE FLORA OF THE COAL FORMATION. 427 



the cell walls (C, c). It is not distinguishable from that of Finite* 

 (Dadoxylon) Brandlingii of Witham, or from that of the specimens 

 figured by Professor Williamson. The wood and transverse partitions 

 are perfectly silicified, and of a dark-brown colour. The partitions are 

 coated with small colourless crystals of quarts and a little iron pyrites, 

 and the remaining spaces are filled with crystalline lamina? of sulphate 

 of barytcs. 



Unfortunately this fine specimen does not possess enough of its 

 woody tissue to show the dimensions or age of the trunk or branch 

 which contained this enormous pith. It proves, however, that the pith 

 itself has not been merely dried and cracked transversely by the elon- 

 gation of the stem, as appears to be the case in the Butternut (Juglans 

 cincrea), and some other modern trees, but that it has been condensed 

 into a firm epidermis-like coating and partitions, apparently less de- 

 structible than the woody tissue which invested them. In this speci- 

 men the process of condensation has been carried much farther than in 

 that described by Professor Williamson, in which a portion of the un- 

 altered pith remained between the Sternbergia cast and the wood. It 

 thus more fully explains the possibility of the preservation of such 

 hollow-chambered piths after the disappearance of the wood. It also 

 shows that the coaly coating investing such detached pith-casts is not 

 the medullary sheath, properly so called, but the outer part of the con- 

 densed pith itself. 



The examination of this specimen having convinced me that the 

 structure of Stembergiaj implies something more than the transverse 

 cracking observed in Juglandacea?, I proceeded to compare it with 

 other piths, and especially with that of Cecropia peltata, a West Indian 

 tree, of the natural family Artocarpaceae, a specimen of which was 

 kindly presented to me by Professor Balfour of Edinburgh, and which 

 I believe has been noticed by Dr Fleming, in a paper to which I have 

 not had access. This recent stem is two inches in diameter. Its 

 medullary cylinder is three-quarters of an inch in diameter, and is lined 

 throughout with a coating of dense whitish pith tissue, one-twentieth of 

 an inch in thickness. This condensed pith is of a firm corky texture, 

 and forms a sort of internal bark lining the medullary cavity. Within 

 this the stem is hollow, but is crossed by arched partitions, convex 

 upward, and distant from each other from three-quarters to one and a 

 quarter inch. These partitions are of the same white corky tissue 

 with the pith lining the cavity; and on their surfaces, as well as on 

 that of the latter, are small patches of brownish large-celled pith, being 

 the remains of that which has disappeared from the intervening spaces. 

 Each partition corresponds with the upper margin of one of the large 



