222 Royal Society : — 



PROCEEDINGS OF LEARNED SOCIETIES. 



ROYAL SOCIETY. 



March 26, 1874. — Joseph Dalton Hooker, C.B., President, iu the 



Chair. 



" On the Organization of the Fossil Plants of the Coal-measures. 

 —Part VI. Perns." By W. C. Williamson, F.R.S., Professor of 

 Natural History in Owens College, Manchester. 



The author called attention to the various methods of classify- 

 ing the fern-stems and petioles of the Coal-measures adopted by 

 Cotta, Corda, Brongniart, and others, aud to the difficulties which 

 attend those methods. Some of those difficulties had been already 

 felt and partially removed by M. Brongniart. All the generic 

 distinctions hitherto adopted were based upon variations in the 

 form, number, and arrangement of the vascular buudles. These 

 elements vary so much, not only in different species of the same 

 genus, but in different parts of the same petiole, as to make them 

 most untrustworthy guides to generic distinctions. The conse- 

 quence has been an enormous multiplication of genera ; but, 

 notwithstanding their number, the author found that if he adopted 

 the methods of his predecessors he would have to establish addi- 

 tional ones for the reception of his new forms. Under these 

 circumstances he decides that it will be better to include the 

 entire series of these petioles, provisionally, under the common 

 generic term of Rachiopteris. This plan dispenses with a number 

 of meaningless genera, and is rendered additionally desirable by 

 the circumstance that all the petioles to which these numerous 

 generic names have been applied belong to fronds which have 

 already received other names, such as Pecoptens, Sphen&pteris, Sec. ; 

 only the structure of fronds found in the shales, and their respective 

 petioles of which we have ascertained the structure, have not yet 

 been correlated. 



As a preparation for the present investigation, the author made 

 an extensive series of researches amongst recent British and foreign 

 fern-stems and petioles, with the object of ascertaining not only 

 the modifications in their arrangements in different parts of the 

 same plant, but especially of studying the modes in which se- 

 condary and tertiary vascular bundles were derived from the 

 primary ones. This inquiry led him over the ground previously 

 traversed by M. Trecul and, so far as British ferns were concerned, 

 by Mr. Church. 



The most common general forms exhibited by transverse sections 

 of these bundles in recent petioles may be represented by the 

 letters H, T, U, and X. As a general rule, the secondary bundles 

 are given off from that part of the primary one which happens to 

 be nearest to the secondary rachis to be supplied. Thus in some 

 cases the upper arms of the X will merely be prolonged and their 



