1 68 STUDIES IN FOSSIL BOTANY 



known as Halonia — has certain points in common with 

 the Ulodendroid branches, but presents a different 

 appearance. The Halonial branch, which, though on 

 the whole smaller than Ulodendron, is often several 

 inches in diameter, is characterised by bearing a number 

 of prominent knobs or tubercles, most often spirally 

 arranged (see Fig. 68, A). The general surface is 

 usually badly preserved, the specimens having evidently 

 been partially decorticated before fossilisation. Where, 

 however, the external characters are well exhibited, so 

 as to show the leaf-bases clearly, they prove that the 

 specimens belonged to Lepidophloios, though it is quite 

 possible that the Halonial condition may have also 

 occurred in the true Lepidodendra. Halonial branches 

 have been found in connection with the ordinary 

 vegetative stems of Lepidodendreae, though whether of 

 Lepidodendron or of Lepidophloios could not in all cases 

 be determined — a point, however, which is of secondary 

 importance. The fact that the Haloniae occurred as 

 ultimate branches of the dichotomous stem, 1 quite 

 disposes of the idea, once maintained by some French 

 writers, that they were of the nature of roots or 

 rhizomes. 



As regards the anatomy, the main Halonial axis 

 may either have in all respects the structure of an 

 ordinary vegetative stem, or may differ from it in the 

 absence of a medulla. The latter was the case in a 

 Halonial branch of the Arran species, Lepidodendron 

 Wunschianum, investigated by Williamson. 2 The 



1 See Williamson, "Organisation, etc.," Part xii. , Plates iii., iv., 1883. 



2 " Organisation, etc.," Part xii. 1883. This species was perhaps a 

 Lepidophloios. 



