148 W. Carnithers — Halonia and Lepidodendron. 



standing the accumulation of evidence as to the foliar appendages of 

 Halonia, Mr. Binney not only completely adopts Mr. Dawes' sug- 

 gestion as to the root-nature of this fossil, but he comes to the 

 conclusion that E.alonia regidaris is the root of Lepidodendron 

 Harcourtii. 



Scarcely any two authors have hitherto agreed as to the interpi'eta- 

 tion of these fossils. Lindley and Hutton considered them to be Con- 

 iferous. They have since been invariably placed amongthe Cryptogams. 

 Dawes and Hooker supposed they might be Lepidodendroid roots, 

 while Binney maintains they are roots of Lepidodendron Harcourtii. 

 Eichwald thinks the stems were closely covered with scales, and 

 that the true leaves were borne on the tubercles, while Brongniart 

 considers that the smaller scars were true leaves, and the tubercles 

 rudimentary roots which have not yet penetrated the bark ; Golden- 

 berg that they were aborted branches, and Von Roehl and Schimper 

 that they were the points of attachment of the fruits. And lastly 

 Feistmantel is almost certain that Halonia has no existence as a 

 genus, and should be incorporated in Lepidodendron. 



To appreciate the meaning of the fossils included under the name 

 Halonia, one must first realize the internal structure of the stem, and 

 the progress of decay and fossilization in the dead plant. The 

 observations of Mr. Dawes, in the paper referred to,^ establish that 

 the organization of the stem agrees with that of Lepidodendron, and 

 consequently consists of an axis composed externally at least of scalari- 

 form tissue, surrounded by a considerable thickness of delicate paren- 

 chyma, which gradually alters outwards into the regularly arranged 

 and thick- walled prosenchyma of the bark. On the death of the plant 

 the delicate parenchyma, forming the inner portion of the cortical 

 tissues, first decayed. The axis enveloped in this soft mass followed, 

 and last of all the more enduring external bark. The more common 

 specimens of Halonia are amorphous casts of the interior of the 

 cortical layer, which exhibit on their surface the elevated tubercles, 

 as well as the small punctiform scars of the leaf bundles. Frequently 

 these latter scars are placed at the apex of a little tubercle ; this has 

 been produced by the substance of the cast penetrating the small 

 passage in the outer bark through which the vascular bundle passed. 

 The parenchyma which suriounded and accompanied the bundle 

 having decayed had left an empty cavity which was easily filled from 

 the interior. The Knorria condition of normal Lepidodendroid 

 branches and stems is, as I have elsewhere explained,^ precisely similar 

 to this state of Halonia. The specimen with the remarkably regular 

 tubercles figured by Lindley and Hutton ("Fossil Flora," pi. 228) 

 as h. regularis is in this condition, as well as Binney 's specimen of 

 the same (Palaeontographical Society, 1872, pi. xviii.), and that 

 figured on the accompanying Plate at Fig. 2. 



Where the specimen was buried in shale, the bark is generally 

 converted into coal, and exhibits the appearance of the specimen 

 drawn in Fig. 3 of the Plate, where the leaf bases are seen on. the 



1 T'repared sections of Halonia in the British Museum confirm the observations of 

 Mr. Dawt-s. 



2 Journal of Botany, vol. vii. (1869), p. 153, plate 93. 



