80 



FOSSIL PLANTS. 



Before leaving the subject of the structure of the stem of Lepidodendron, it will be as 

 well very briefly to consider the dichotoraization of the stem of this plant. This appears 

 to have been of the same character in Lepidodendron, SigiUaria vascularis, Halonia, and 

 probably other similar plants. It is like that which prevails in Lycopodiacese as described 

 by Brongniart^ as follows : — " Ce mode de ramification me parait extremement rare parmi 

 les plantes appartenant a d'autres classes du regne vegetal, car toutes les plantes phanero- 

 games qui offrent des tiges dichotomes doivent cette apparence ou a un rameau reellement 

 lateral et secondaire, qui a pris un accroissement egal au rameau principal, ou a deux 

 rameaux lateraux, opposes ou alternes et rapproches, qui se sont seuls developpes tandis 

 que la tige principale s'est transformee en un simple pedoncle floral, ou bien a subi un 

 avortement complet. 



" Dans ces divers cas un des rameaux ou meme tous les deux sont d'nn ordre dif- 

 ferent de la tige a laquelle ils font suite, et ils naissent de I'aisselle d'une feuille inseree 

 sur cette tige. Dans les Lycopodiacees, ou contraire, le developpement est continu, et la 

 tige tout entiere se divise en deux faisceaux, comme on le voit quelquefois parmi les 

 plantes phanerogames, dans les tiges monstrueuses, dites fasciedes, qui seules me paraissent 

 ofl'rir un mode de division analogue, malgre son irregularite, a celui des Lycopodiacees." 

 This mode of division in the stem has not to my knowledge been hitherto noticed, 

 although collectors must have observed instances of it. 



§ 2. The Specimen {Lepidodendron Harcourtii), No. 32. Plate XIV, 



figs. 1, 2, 3. 



Specimen No. 32 (Plate XIV, fig. 1, natural size) is the transverse section of a stem 

 of Lepidodendron Harcourtii, found by me in the Black-shale-ironstone in the lower part 

 of the Middle Coal-measures at Hady, near Chesterfield. It is of an oval form, and 

 measures three inches across its major and one and a half inches across its minor axis. 

 The outside is marked with prominent rhomboidal scales, measuring three eighths of an 

 inch one way and two eighths of an inch the other. The fossil, composed of clay-ironstone 

 of a black colour, is enveloped in a coating of bright coal, and shows no trace of structure 

 except in the two horseshoe-shaped bodies in the inside. At the first glance these might 

 have been considered to have been accidentally introduced after the interior of the stem 

 had been decomposed and removed ; but the occurrence of similar axes in the stems of 

 Sigillaria vascularis and Halonia regularis, hereinafter described, shows that this is very 

 improbable, if not impossible. The two axial bodies occur in about the middle of the 

 specimen, and at about equal distances from the sides, each measuring two eighths of an 



1 ' Ilistoire des Vegetaux fossiles,' Tome ii, pp. 3, 4. 



