248 Prof. W. C. Williamson on the [Mar. 26, 



March 26, 1874. 

 JOSEPH D ALTON HOOKER, C.B., President, in the Chair. 



The Presents received were laid on the table, and thanks ordered for 

 them. 



The following Papers were read : 



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

 measures. Part VI. Ferns." By W. C. WILLIAMSON, F.R.S., 

 Professor of Natural History in Owens College, Manchester. 

 Received March 18, 1874. 



(Abstract.) 



The author called attention to the various methods of classifying the 

 fern-stems and petioles of the Coal-measures adopted by Cotta, Corda, 

 Brongniart, and others, and 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 vas- 

 cular bundles. 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 consequence 

 has been an enormous multiplication of genera ; but, notwithstanding 

 their number, the author found that if he adopted the methods of his pre- 

 decessors he would have to establish additional 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, uuder the 

 common generic term of Racfiiopteris. This plan dispenses with a number 

 of meaningless genera, and is rendered additionally desirable by the cir- 

 cumstance that all the petioles to which these numerous generic names 

 have been applied belong to fronds which have already received other 

 names, such as Pecopteris, Sphenopteris, &c., only the structure of fronds 

 found in the shales, and their respective petioles of which we have ascer- 

 tained the structure, have not yet been correlated. 



As a preparation for the present investigation, the author made an ex- 

 tensive 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 secondary 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 



