37o ARTHUR L MASLEN [may 



the latter genus, the vegetative characters are very completely known, 

 and they approach the cycads even more closely, since here the 

 cycadean type of vascular bundle is found, not merely in the stem but 

 in the petiole also. Moreover, in Poroxylon secondary wood was 

 formed in the leaf, and what is still more interesting is the fact that 

 the latter organs (the leaves) appear to approach the familiar Coal 

 Measure forms of Cordaites. On this point Dr. Scott points out that 

 Poroxylon is " known only from the Upper Carboniferous, so we 

 cannot regard it as in any way representing the ancestors of the far 

 more ancient Cordaiteae. The genus suggests, however, the possibility 

 that the Cordaiteae and the Cycadeae (taking the latter term in its 

 wide sense) may have had a common origin among forms belonging to 

 the filicinean stock." 1 



MM. Bertrand and Renault, however, do not recognise filicinean 

 affinities in Poroxylon. "lis n' out aucun rapport avec les 

 Pteridophytes," and they attempt to derive not only Poroxylon but 

 Lyginodendron and the cycads themselves from the lycopods. 

 But, as Dr. Scott again points out, this view is no longer tenable. 

 Both recent cycads and their fossil allies (Bennettiteae, Lyginoclendreae, 

 Medulloseae) abound in fern-like characters, and have simply nothing 

 in common with Lycopods. . . . Recent work has completely confirmed 

 Williamson's original view as to the fern-affinities of these fossil 



» 2 



genera. 



Count Solms-Laubach has also described the structure of a some- 

 what curious ally of Lyginodendron from the Culm of Balkenberg, 

 under the name of Protopitys Buchiana. 3 Here the plant bore 

 distichous leaves, and the central cylinder has the form of an ellipse 

 composed of a large pith surrounded by a thin continuous ring of 

 primary wood, the whole being surrounded by a considerable 

 thickness of secondarily developed xylem. From the extremities of 

 the long axis of the ellipse the petiolar bundles are given off alternately 

 from either end. Solms-Laubach himself considers this type as 

 representing a special group — the Protopityeae, but he is in general 

 agreement with Williamson and Scott in thinking that Protopitys 

 constitutes another of the types which are intermediate between the 

 Filicineae and the gymnosperms. 



Returning now to the genus Heterangium, founded by Corda in 

 1845, and which has a wider range in time than Lyginodendron, and 

 of which the best specimens have been obtained from the Burntisland 

 beds at the base of the Carboniferous system, we have a type which at 

 first sight seems very different from Lyginodendron, but which, on closer 



1 Report British Assoc, 1896 (Pres. Add. Botanical Section), p. 1008. 



- "The Anatomical Characters presented by the Peduncle of Cycadaceae," Annals of 

 Botany, vol. xi. pp. 415, 416. 



3 "Ueber die in den Kalksteinen des Kulm von Glatzisch-Falkenberg in Schlesien 

 enthalteiien Structur-bietenden Pflarizenreste," II. Abhandlung. Botan. Zcitung, 1893, 

 pp. 197-208. 



