172 The Bota?iical Gazette. tf une ' 



On the organization of the fossil plants of the 



Coal-measures. x 



DAVID WHITE. 



[The following review contains so much of anatomical importance that we 

 give it this more conspicuous place. — Eds.] 



The observations recorded in these three memoirs, while 

 confined chiefly to types, most of which have been treated 

 more or less in the preceding parts, are hardly less remarkable 

 for the information they bring to bear on the mode of the 

 formation of the medulla and the development of exogenous 

 growth in certain Carboniferous cryptogams, than for the proof 

 they furnish of the existence of an exogenous growth among 

 the Carboniferous ferns. 



Part XV throws new light on the structure of the rhizomes 

 and petioles belonging to Corda's genera Zygopteris and 

 Anachoropteris, as recognized by Renault, Stenzel, and others, 

 which Williamson shows to be generically equivalent. For 

 these he prefers the name Rachioptcris proposed by himself in 

 1874 (Pt. VI, p. 677) "for a considerable number of these 

 objects which appeared to be either rhizomes or petioles 

 of ferns," for the reason that an examination of the struc- 

 ture of living ferns, classified by their fructification, shows 

 that "no classification of fossil ferns based solely on 

 the characters revealpd in transverse sections of their 

 petiolar bundles can be of value." Neither Prof- 

 Williamson nor several other recent authors, seems to 

 be aware of the coincident fact that Dawson in 1861 

 (Q. J. G. S. L., xviii, p. 323), with equal appropriate- 

 ness, proposed the new genus Rhachiopteris "to include such 

 Devonian stipes as indicate the existence of distinct species 

 of ferns, of which the fronds have perished." Schimper does 

 not seem to have known of Dawson's genus when he estab- 

 lished his Rhacopteris (Traite, I, 1869, p. 481), based on the 

 character of the fronds. Incognizance of these facts and the 

 too common mis-spelling of the generic names have caused 

 much confusion in the nomenclature. 



To a fine species, from the Halifax deposits, related to 

 Renault's Anachoropteris Dccaisnii, Williamson gives the 



1 Williamson, W. C— On the organization of the fossil plants of the Coal- 

 measures. Phil. Trans. Roy. Soc. London. Part XV, vol. 180 (1889) B. pP 

 155-168, pi. i-iv. Part wi. 1. c, pp. 195-214, pi. v-viii Part xvii, op. en- 

 voi 181 (1890) B. pp. 8JM06, pi. xii-xv. 



