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X. On the Organization of the Fossil Plants of the Coal-measures. — Part II. Lycopodiaceae: 
Lepidodendra and Sigillarice. By W. C. Williamson, F.B.S., Professor of Natural 
History in Owens College, Manchester. 
Received June 13, — Read June 15, 1871. 
In 1849, when M. Brongniart published his ‘ Tableau des genres des Vegetaux Fossiles,’ 
he admitted into his series of Acrogenous Cryptogams a family of Lepidodendra, in which 
he included Lepidodendron, Ulodendron, Megaphyton, Halonia, Lepidophloios , and 
Knorria. At the same time he recognized as Gymnospermous Dicotyledons , a family of 
SigillaricU, including Sigillaria, Stigmaria, Syrmgodendron, and Diploxylon. He distin 
guished these two groups by supposed differences in the structure of the ligneous 
cylinder surrounding the pith. Speaking of this structure in the Lepidodendroid plants, 
he says, “ Non-seulement il est continu et non divise en faisceaux par des rayons medul- 
laires, caractere que j’ai indique dans plusieurs families tres-diverses des dicotyledones, 
mais les elements qui le composent ne forment pas de rangees rayonnantes. Cette 
absence de direction radiee dans la disposition relative du tissu ligneux me parait un 
caractere tres-essentiel, car elle indique la formation simultanee de ce tissu, et non sa 
formation successive du dedans au dehors, caractere de la zone ligneuse des dicoty- 
ledones”*. Describing his family of Sigillarise, he says, “ Le caractere essentiel de ces 
plantes, c’est de presenter, dans l’interieur de leur tige, un cylindre ligneux entierement 
compose de vaisseaux rayes ou reticules disposes en series rayonnantes, separes en 
general par des rayons medullaires, ou par les faisceaux vasculaires qui, de l’etui medul- 
laire se portent vers les feuilles”f. He further adds, “ Les principaux genres de cette 
famille, ceux qui appartiennent sans aucun doute a de vraies tiges, presentent, en dedans 
du cylindre interieur, sorte d etui medullaire, continu et sans rayons medullaires dans le 
Diploxylon , clivise en faisceaux correspondant aux faisceaux principaux du cylindre 
ligneux dans le Sigillaria”'f 
I have long been engaged upon the study of the plants referred to in the above 
extracts. I have not only had the opportunity of examining numerous specimens in 
the cabinets of friends, but in nearly every instance I have literally dissected each 
specimen described, in my own lathe, so as to avoid, as far as possible, all sources of 
error. The result is that I am now in a position to demonstrate the complete unity of 
the plants which M. Bkongniart has separated so widely, and to show that the transition 
from one form to another is so gradual as to necessitate the inclusion of the entire 
series in the Lepidodendroid family. 
* Loc. cit. p. 39. f Loc. cit. p. 55. t Loc. cit. p. 55. 
MDCCCLXXII. 2 D 
