62 Boyal Society : — • 



diating lines proceeding from within outwards. The outer bark 

 consists of narrow, elongated, prosenchymatous cells, having very 

 thick walls ; at intervals, corresponding with the spaces between 

 the successive verticils of leaves in the ordinary examples of Astero- 

 plujllites, we find distinct nodes where the bark expands into lenti- 

 cular disks. The vascular axis passes through these nodes without 

 undergoing any visible change, either in the position of its vascular 

 layers or ingi^'ing off vessels to the nodes or their appendages. The 

 thin peripheral margin of each node sustains a verticil of the slender 

 leaves of Asteroijluillites, of which there are about twenty-six in 

 each verticil. The aspect, dimensions, and arrangements of these 

 leaves correspond exactly with what is seen in the ordinary speci- 

 mens found in the coal-shales. Transverse sections of them exhibit 

 a single thick central midrib, but no traces of vascular tissues have 

 hitherto been found in them. 



The laminje of the vascular axis are separated by numerous 

 medullary rays of small size ; these rarely exhibit more than four 

 or five cells in any vertical series, and usually but one or two. 

 The exterior of the bark is deeply indented in each internode by 

 three very deep superficial grooves, each one of which occupies the 

 side of the stem corresponding with a concavity of the central 

 ti'iangle of the vascular axis. These grooves, which are sometimes 

 double instead of single, extend from node to node, but do not 

 indent the nodal disks. Owing to the great depth to which these 

 penetrate the bark, they give a very characteristic tripartite aspect 

 to each transverse section of these stems. 



The Burntisland tj'pe agrees with the Lancashire one in all its 

 leading features of structure and growth ; but its vessels are all 

 barred instead of being reticulated, and the author has not met 

 with such beautiful examples of its nodal disks as he has done in 

 the case of the other form ; neither has he seen its leaves attached. 

 On the other hand, he has found specimens of much larger dia- 

 meter than any that have hitherto been detected in Lancashire, 

 exhibiting in an exquisitely beautiful manner the characteristic 

 peculiarities already referred to. The author has also obtained one 

 section from this locahty in which a branch is given off. The 

 vessels of this divergent organ are derived from the central por- 

 tion of one of the segments of small vessels, seen in the trans- 

 verse sections, which proceed from one of the angles of the central 

 triangle. 



Having elucidated the details of the aerial stems, the author 

 proceeds to examine such organs of fructification as appear to 

 belong to these plants, commencing with the Volkmannia Dawsonr 

 which he described at length in the Transactions of the Philoso- 

 phical Society of Manchester in 1871. This is a verticillate strobilus 

 with a central vascular axis, of which latter transverse sections 

 exhibit a close correspondence with the triangular bundle of Astero- 

 phiillites, being also triangular, with concave sides and truncate 

 angles. But in order to adapt this primary fibrovascular bundle 

 to the requirements of the fruit, each of the truncate angles is 



