HALONIA. 95 



generally been taken for Halonia regularis ; but, when clothed with its epidermis, it 

 clearly resembled, and might be taken for, a Stigmaria. 



VII. Concluding Remarks. 



Those portions of the Hesley Heath specimen in which the structure of the stem had 

 been destroyed have fortunately been preserved in the Dudley specimen described in this 

 Monograph, so that it may be now considered that we possess a knowledge of the structure 

 of the whole of the stem of Lepidodendron Harcourtii. 



In addition to the reasons given at page 37 for believing that Sigillaria and Lepi- 

 dodendron were different, though allied, plants, I consider that the Dudley specimen of 

 Lepidodendron Harcourtii clearly proves that it had a medulla of orthosenchyma, whilst 

 the Sigillaria vascularis and Lepidodendron vasculare had, in the place of such tissue, 

 large scalariform tubes, sometimes but not always mixed with orthosenchyma. Moreover, 

 the central woody axis of Sigillaria vascularis was arranged in wedge-shaped masses, and 

 penetrated by medullary rays, thus differing altogether from the entirely vascular zone 

 constituting the woody axis of Lepidodendron, either Harcourtii or vasculare. The 

 vascular bundles proceeding from the outside of the woody cylinder to the leaves, the zone 

 of lax parenchyma gradually increasing in strength, and afterwards passing into elongated 

 utricles or tubes, and having a radiating arrangement at its outside, as well as the 

 epidermis, all appear to have been much the same in structure in both Lepidodendron 

 and Sigillaria. 



It appears from my specimens, hereinbefore described, that Lepidodendron Harcourtii, 

 Sigillaria vascularis, and Halonia regularis, had all a similar mode of dichotomizing, and 

 that the division of the pith and woody axis was much the same in these three plants. The 

 facts are given as they appear from an examination of the specimens, and are left for the 

 consideration of the physiological botanist, who is much abler than myself to investigate 

 the system of dichotomization of ancient plants by the phenomena observed in living 

 Lycopodiacece . 



I have always had a doubt that Lepidodendron had the Stigmaria jicoides for its root, 

 such as was proved to be the case with large, ribbed, and furrowed Sigillaria ; but I 

 saw the probability of Mr. Dawes' view, that Halonia regularis might prove to be the 

 root of Lepidodendron, both on account of its frequent bifurcations and on account of 

 other characters, quite independent of the similarity in structure of the two plants. 



The researches of Mr. Richard Brown and Professor Schimper led me to expect that 

 Lepidodendron, as well as Knorria, had a Stigmarioid root. My own observations, and 

 the specimens here described, lead me to conclude that Halonia regularis is the root of 

 Lepidodendron Harcourtii, but not the root of Sigillaria, that being, as was before stated, 

 Stigmaria jicoides. It is seen in the description of the specimens in this Monograph how 



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