202 



On the Fossil Plants of the Coal-measures. [Mar. 7, 



vascular bundles pass outwards to the leaves ; these bundles have pro- 

 tected the contiguous cells above and below them from the pressure of the 

 enlarging ligneous vessels and limited their absorption. Both these and 

 the smaller ordinary rays pass outwards in horizontal and parallel lines. 

 The evidences of an exogenous mode of growth afforded by these young, 

 half-developed layers of wood is clear and decisive. 



The Burntisland deposits are full of fragments of strobili, especially of 

 torn sporangia and of macrospores. Several fine Lepidostrobi have been ob- 

 tained like those to which the fragments have belonged, and which the 

 author believes to have been the fruits of the stems described. The struc- 

 ture of these strobili is very clear and of interest ; the primary branches 

 from the central axis subdivide, so that each sporangium rests upon a sepa- 

 rate bract, from the upper surface of which a vertical lamina arises, and, 

 extending the entire length of the sporangium, ascends far into its interior, 

 •where it bifurcates. The cellular walls of the sporangium blend with the 

 bract along each side of the base of this sporangiophore. The microspores 

 occupy the upper part of the Lepidostrobus, and are usually triplospores, 

 sometimes tetraspores. The macrospores occupy the lowermost spo- 

 rangia, are of large size, and are very remarkable from having their external 

 surfaces clothed with numerous projecting caudate appendages, each one of 

 which is slightly capitate at its extremity. So far as the author is aware, 

 this is an undescribed form of macrospore. 



Two new forms of Lepidodendron are described from the Oldham beds, 

 in one of which the medullary axis attains to an unusually large size, even 

 in the young shoots ; whilst the other is remarkable for the magnitude of 

 its leaves. It is obvious that the plant which' is. the chief subject of the 

 memoir is a true example of Corda's genus Diploxylon, so far as its woody 

 axis is concerned ; whilst its bark and leaves are those of a Lomatophloios, 

 and its slender twigs are Lepidodendra. The author also points out the 

 probability that the plant had a true Stigmarian root. 



The structure of these fossil types is compared with that of recent 

 LycopodiacecB. The vascular medullary cylinder is shown to be an aggre- 

 gation of the foliar vascular bundles, so that the vascular connexion be- 

 tween the leaves and the stem is maintained exclusively by means of these 

 vessels, which thus correspond most closely with the central vascular axes 

 of living Lycopods. On the other hand, the exogenous layers do not 

 communicate directly with the leaves in any way — but are homologous 

 with the corresponding layers in the Stigmarian root, in which latter they 

 receive the vascular bundles from the rootlets. The medullary cylinder 

 does not enter the roots, but appears to terminate at the base of the stem, 

 though the pith is prolonged through them. Hence it seems probable 

 that the nutritive matters were taken up from the soil by the Stigmarian 

 rootlets, that they ascended into the Diploxyloid stem through the exoge- 

 nous layer, but that, in order to reach the leaves, if conveyed by the vessels 

 and not by the cellular tissues, they had to be transferred by endosmosis to 



