i!i 



THE CARBONIFEROUS FLORA, 



159 



6. Leioderma, Goldonborf?. Type, S, Sydjiermis, Dawson. — 

 Ribs obsolete. Cortical and ligneous surfaces strh^o. Vascular 

 scars double. elonf,'atc loti^itudiniilly, and alike on co:(ical and inner 

 surfaces. Areoles in rows and distinct; stigmaria-roots striate, with 

 small and distinct areoles. 



• 6. ('Inthrnrin, Hron^jniurt. Type, aS". Mennrdi, Brongniart. — 

 Areoles li(!XHf,'()nuI, iiot in distinct rows, but havinp^ a spiral apjjcar- 

 ance. Some of tlie |)lunts ustuilly referred to this j^roup are probalily 

 branches of Favularia. (Jthers are evidently fragments of plants 

 of the genus Lepidojihloios. 



S. Internal Structures of Sujillaria-StemH. 



1 long a^jo pointed out, on the evidence of the external markings 

 and mode of growth, that the stems of Sigillarim must have been 

 exogenous, and this conclusion has now been fully confirmed by the 

 microscopic researches of VVillianison, not only in the case of >SV/yi7- 

 lariiB, but of Lepidodetidra and ( 'alamodendra as W(!ll. (-'onfining 

 myself to my own observations, three types of Siffillanai are known 

 to me l)y their internal structures, though I cannot certainly corre- 

 late all of these with the exter.ial markings referred to above. 



1. Diplnxylon, in which the stem consists of a snuUl internal 

 axis surrounded by a very thick inner bark and a dcmse outer cortex. 

 A fine example from the South Joggins is thus described : * 



"The axis of the stem is about six centimetres in its greatest 

 diameter, and consists of a central pith-cylinder and two concen- 

 tric coats of scalariform tissue. The pith-cylinth^r is replaced 

 by sandstone, and is about one centimetre in diameter. The inner 

 cyliiuh^r of scalarifortn tissue is perfectly continuous, not radiated, 

 and about one millimetn! in thickness. Its vessels arc somewhat 

 crushed, but have liecn of large diameter. Its outer surface, which 

 readily separates from that of the outer cylinder, is striated longi- 

 tut"; lal'y. The outer cylinder, which institutes by much the 

 largest part of the whole, is also compose(l of scalariform tissue; 

 but thin is radially arranginl, with the individual cells (jua<lraiigular 

 in cross-section. The cross-bars are similar f>Ti all the sides and 

 usually simple and straight, but sometimes l)ranching or slightly 

 reticulated. The wall intervening between the bars has extremely 

 delicate longitviclinal waving lines of ligneous lining, in th(! manner 

 first described by Williamson as occurring in the scalariform tissue 

 of certain Lepidodendra. A few small radiating spaces, partially 



• " Journal of the Geological Society of London," Novciuber, '7. 



