LEPIDODENDRON. 



79 



in texture) to that of tlie medulla traversing the great mass of parenchyma {e), which 

 forms the chief portion of the stem. 



Fig. 4 shows a longitudinal section of an outer portion of the stem (magnified twelve 

 diameters), in which are displayed the coarse parenchymatous tissue {e), passing into 

 elongated utricles and tubes (/), that nearly resemble true vascular tissue, but show no 

 markings on their walls, and the epidermis (y), converted into coal, about twice the thick- 

 ness of the radiating zone. 



Fig. 5 (magnified twenty-four diameters) is a partly transverse section of one of the 

 vascular bundles, taken near the outside of the stem. In structure, whether we consider 

 the vascular bundle of scalariform tubes, the orthosenchymatous tissue so often wanting, 

 the light-coloured zone of fine parenchyma, and the outside of coarse parenchyma, it very 

 much resembles a transverse section of a rootlet of Stigmaria, as figured and described by 

 me in the 'Quart. Journ. Geol. Soc.,' vol. vi, pp. 18, 19. This structure had long 

 previously been made out by Professor Goeppert.^ 



Fig. 6 (magnified five diameters) is a section of a portion of the outside of the stem, 

 showing the coarse parenchymatous tissue, passing into the elongated utricles (or tubes), 

 arranged in radiating series, together with a portion of the epidermis, and one of the outer 

 bundles near to its passage into a leaf. 



If we separate the various structures already described into two series, the one axial 

 and the other epidermal, we have (1) an axis, composed of orthosenchymatous tissue, 

 (2) a woody cyhnder, formed of an inner zone of coarse vascular tissue and an outer one 

 of finer vascular tissue, from the latter of which originate (3) the vascular bundles, passing 

 to the leaves, belonging to the first, and (4) the zones of fine and coarse parenchyma, the 

 latter passing into (5) elongated utricles or tubes, resemljhng those found in Sigillaria 

 vascularis, Stigmaria, and Halonia, and (G) the outer bark, belonging to the second. 



This specimen, to a great extent, confirms the views of Brongniart on the structure of 

 the stem of Lepidodendron Harcourtii, as restored by him from the Hesley Heath 

 specimen ; but the medulla is in a much better state of preservation than it was in the 

 Rev. Mr. Harcourt's fossil. The vascular bundles are shown to be enveloped in a zone of 

 orthosenchymatous tissue, which Brongniart, it appears, did not notice. The line of 

 demarcation betwixt the inner and finer parenchyma and the coarser and outer zone is 

 found to be nearly imperceptible, and not so well defined as he represented it. The 

 outer radiating series, moreover, is composed of much longer utricles (or tubes) than those 

 he restored. Altogether the characters of Mr. Dawes' specimen, though in a better state 

 of preservation than that of Hesley Heath, do not, in my opinion, vary sufticiently from 

 that plant to be made the basis of a new species ; therefore it has been considered desirable 

 to class this specimen under Lepidodendro?!. Harcourtii. 



' ' Genera Plant. Foss.' (Sligmaria), p. 29. 



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