96 



FOSSIL PLANTS. 



much Stigmaria resembles Halonia in its external appearance, with the exception of 

 its tendency to bifurcate, which Stigmaria does not do after it has assumed its ordinary 

 characters, and that it is very difficult, if not impossible, to distinguish an imperfect spe- 

 cimen of one of these roots .from the other, although their internal structure differs as 

 much as that of Lepidodendron Harconrtii does from Siyillaria vascularis. Li short, it nmst 

 be considered that Halonia regularis is merely a Sligmaria with its epidermis removed. 



Now, when we compare the internal structure of Halonia regularis with that of 

 Lepidodendron HarcourtU, we find they are the same in every particular. The medulla, 

 composed of orthosenchyma, is the same in both plants ; so also the interior and exterior 

 of the woody cylinder, composed of larger and smaller barred vessels — the vascular bun- 

 dles leading to the leaves — the lax and delicate parenchyma gradually increasing in 

 strength until it passes into elongated utricles (prosenchyma), arranged in radiating series 

 —and the epidermis forming the exterior, are all alike in Halonia and Lepidodendron; 

 therefore, as to identity of structure, and so far as that is of any value, we are led to con- 

 clude that Halonia regularis is the root of Lep)idodendron HarcourtU. Up to this time, 

 however, I have not heard of their having been found absolutely united to each other, as 

 was the case with Sligmaria and Sigillaria. 



In my examination of the Lancashire Coal-measures I have generally found Halonia 

 regularis associated with Lepidodendron. This is the case in the Peel Quarry, where both 

 these fossil plants are found in about the same relative proportions. A similar result is 

 obtained in the Upper Poot seam of Oldham and the BuUion Coal of Burnley and its 

 vicinity ; but in the Upper Brooksbottom seam Halonia occurs more frequently than 

 Lepidodendron, so far as my experience in collecting the fossil plants in this seam of coal 

 has extended. In many districts, no doubt, Lepidodendron is found in great abundance, 

 with few or no traces of Halonia regularis ; but in such cases we always meet with nume- 

 rous ill-preserved specimens of Sligmaria. In my own experience well-defined specimens 

 of Halonia regularis, showing the quincuncially arranged tubercles, are seldom found 

 except in sandstones, and when the epidermis of the plant has been removed. The reason 

 why they have not been recognized in shales and " binds" is, that they are there 

 compressed with their epidermis on, and have been generally taken for remains of 

 Sligmaria. 



