Prof. W. C. Williamson on Plants of the Coal-Measures. 225 



They may prove to be i-hizomes and roots of the Asterophyllite de- 

 scribed in my last letter to you. 



Of this last genus I have just got an additional number of ex- 

 quisite examples, sJioiving not only the nodes but verticils of the 

 lineai' leaves so characteristic of the plant. These specimens place 

 the correctness of my previous inference beyond all possibility of 

 doubt, and finally settle the point that Asterojihyllites is not the 

 branch and foliage of a Calamite, but an altogether distinct type of 

 vegetation having an internal organization peculiarly its own. This 

 organization is identical in every essential point with that of my 

 Volkmannia Bawsoni already referred to in my previous letter, and 

 which I now do not hesitate to designate Asterophyllites Dawsoni. 

 The peculiar triquetrous form of the young vascular axis of this 

 genus is too remarkable and too distinct from that of all other Carbo- 

 niferous types to be mistaken for any of them, and especially for 

 that of Calamites, with which it has not one single feature of real 

 affinity. 



I have also obtained, partly through the assistance of Messrs. 

 Butterworth and Whittaker, but especially the latter, an instructive 

 series of specimens of the genus Zygopteris, which has recently been 

 made the subject of an important memoir by M. B. llenault, pub- 

 lished in tome xii. of the 'Annales des Sciences Naturelles.' Our 

 Lancashire specimens are of the type which he describes under the 

 name of Z. Lacattii. The French savant has found these plants, in 

 one instance, connected as petioles to a rhizome which he believes 

 to he that of a fern. Our specimens supply some information 

 additional to that published by M. Renault : they appear to me to 

 sustain his idea that they are petioles ; and I have traced in them the 

 origin of the two vascular bundles which he refers to as pores existing 

 in the bark. I find much reason for concluding that they are, as he 

 surmises, the vessels going to the secondary rachis of the pinnules. 

 Our Lancashire specimens are covered with sparse but very distinct 

 hairs that, unlike the ramentaceous form common amongst ferns, are 

 perfectly cylindrical. Whilst I am thus inclined to express my 

 conviction that M. llenault is correct in his views respecting Zygo- 

 pteris, I find it increasingly difficult to distinguish fragments of ferns 

 from those of Lycopods, as also fragments of petioles from those of 

 roots. 



Mr. Nield and Mr. "Whittaker, of Oldham, have just supplied me 

 with two magnificent stems of Calamites of large size. The pith 

 is absent from both, except some slight traces at the node of one 

 of the specimens. I find on dissecting these matured stems that the 

 remarkable arrangements of the vascular structure seen in plate 23. 

 figure 2 of my memoir on Calamites almost entirely disappear in the 

 more external of the exogenous growths. The conspicuous vertical 

 laminae of cellular parenchyma (my primary medullary rays), which 

 separate the woody wedges, rapidly diminish in size as they proceed 

 from within outwards, becoming more or less like the secondary 

 or ordinary medullary rays represented in my fig. 5. ISIany of them, 

 however, retain the evidence of their primary medullary ori»in in 



