8 



Prof. W. C. Williamson. 



[Jan. 6 r 



IV. "On the Organisation of the Fossil Plants of the Coal- 

 measures. Heterangium Tiliceoides (Will.) and Kaloxylon 

 Hookeri." By Professor W. C. W 7 illiamson, LL.D., F.R.S., 

 Professor of Botany in the Owens College and in the 

 Victoria University. Received December 1, 1886. 



(Abstract.) 



Several years ago the author discovered the stems and branches 

 of a remarkable plant in the Carboniferous beds at Burntisland, 

 which he described in the volume of the ' Philosophical Transactions r 

 for 1873, under the name of Heterangium Grievii. This plant dis- 

 played a central axis, in which was combined a curious mixture of 

 cells and vessels. These were surrounded by a vascular zone, with 

 medullary rays, evidently a product of an investing cambium layer. 

 Outside this exogenous growth were a complex series of cortical 

 layers, with various arrangements of vascular bundles going off to 

 supply lateral appendages. The indefatigable industry of my valuable 

 auxiliaries, William Cash, Esq., and Mr. Binns, of Halifax, have 

 supplied a series of specimens which the author soon found to be 

 a new species of Heterangium, to which he gives the name of Heteran- 

 gium Tiliceoides. Whilst the plant exhibits all the features of interest 

 seen in H. Grievii, it has others peculiar to itself. Its central axis 

 corresponds closely with that of H. Grievii. Its exogenous vascular 

 or zylem zone is more fully developed than in the older species, but 

 the most striking features are seen in new structures external to and 

 developed by what has been a cambial zone. The zylem consists of 

 groups of vascular laminse, the inner ends of each of which groups so> 

 converge as to separate the vascular ring into a series of distinct 

 bundles. These are not only separated from each other by primary 

 medullary rays, but as each of these latter passes outwards towards 

 the cortex, it rapidly expands laterally, assuming, in transverse 

 sections, a trumpet- shaped contour. These are in fact true primary 

 phloem rays, as fine as those seen in the shoots of the Lime tree ; 

 hence the specific name of Tiliceoides given to the plant by the author. 



Between these large phloem rays are clusters of phloem, the radial 

 diameter of each of which is co-extensive with the zylem part of the 

 bundle to which it belongs. Each of the zylem-bundles is subdivided into 

 minor groups of two or three vascular laminae, separated by secondary 

 medullary rays, each of which latter can be traced as secondary 

 phloem rays passing radially outwards through the phloem portion 

 of each bundle. The vessels seen both in the vasculo-medullary 

 axis and in the exogenous zone are chiefly furnished with bordered 



