86 FOSSIL PLANTS. 



" There are some other points connected with, and in the constitution of, these fossils 

 that I hope to refer to on a future occasion ; and may perhaps now observe that the 

 medullary column does not, either in the Lepidodendron or Halonia, consist of the usual 

 parenchymatous tissue, but seems to be composed of large quadrangular cells arranged in 

 perpendicular series, and presenting an appearance as though each minute column was 

 confined within a slight membrane or tube. I believe that no such structure has been 

 found to exist in recent vegetation, the nearest approach to it being probably in Psilotum, 

 one of the Lycopod family, and of course incompatible with the idea of this central 

 portion being a true medulla ; these plants must therefore be still further removed from any 

 supposed phanerogamic alliances." 



§ 5. Dr. Hooker, in writing of Lepidodendron? states, " Of the stem, branches, 

 leaves, and fructification, we have thus a satisfactory knowledge, but the nature of their 

 roots is not ascertained. Mr. Dawes, of West Bromwich, to whom I am indebted for 

 much information regarding the structural character of coal fossils, is inclined to regard 

 the species of Halonia as roots of Lepidodendron, on which opinion I have no remarks 

 to offer." Again, on the same page, he observes, " Halonia, another genus of Lepi- 

 dodendrea, is composed of three species, possibly the roots of these or others of the 

 same genus." 



§ 6. Brongniart, in treating of Halonia, writes, 2 



" Halonia, Lind. et Hutt. 



" Les tiges, assez rares et mal connues, qui forment ce genre, offrent, sur les parties qui 

 sont bien conservees, une ecorce, marquee de cicatrices foliaires, disposees comme dans les 

 Lepidodendron; mais la tige presente en outre de gros tubercules coniques disposes 

 en quinconce, et sur lesquels s'etend uniformement Pecorce generale et les feuilles qu'elle 

 supportait. 



" La disposition quinconciale des mamelons ou tubercules qui font saillie sur la tige 

 et la continuitie de leur base avec le reste de l'ecorce de la tige distingue completement ce 

 genre des precedents. Ici les gros mamelons ne paraissent pas des cicatrices, mais des 

 saillies sous-corticales comme celles qui seraient produites par des racines non sorties de 

 dessous l'ecorce." 2 



1 "On the Vegetation of the Carboniferous Period," 'Memoirs of the Geological Survey of Great 

 Britain,' vol. ii, Part II, p. 422, 1848. 



2 ' Tableau des Genres de Vegetaux Fossiles,' p. 43, 1849. 



