170 Mr Seward, Notes on the Binney Collection 



through the periphery of the stem ; in the material at present 

 available we have no evidence as to the fate of the leaf-trace of 

 Megaloxylon after it emerges from the secondary wood of the stem ; 

 it may, however, have entered the petiole in the form of several 

 small exarch bundles, or as a single comparatively large strand. 



Heterangium has been described as possessing a stem which — 

 apart from the secondary growth — " is essentially that of a raono- 

 stelic fern of the Gleichenia type 1 ." In the case of Megaloxylon 

 we may say that the primary stele agrees with that of Lygodium 2 , 

 a monostelic fern with exarch protoxylem. In Lygodium, how- 

 ever, the tracheids are all of the usual tubular form, and possess 

 the ordinary scalariform type of pitting characteristic of ferns ; 

 but apart from these differences the stele of the Schizaceous genus 

 affords a close parallel with that of Megaloxylon. 



The peculiar metaxylem tracheids of the new generic type 

 distinguish the primary xylem of the stem from that of any known 

 plant. The nearest approach to the large and short pitted 

 tracheids is perhaps afforded by the so-called "speichertracheiden 3 " 

 described by Haberlandt, Heinricher and others as modified 

 tracheal elements — often isodiametric in shape — which are met 

 with in the leaves of species of Gapjparis, Centaurea, Euphorbia 

 and other plants in which they serve as elements for the storage 

 of water, and belong to the category of structural peculiarities 

 associated with xerophytism. The abundance of the large me- 

 taxylem tracheids in Megaloxylon and their intimate connexion 

 with the longer leaf-trace elements, lead one to entertain the 

 opinion that this peculiarity in the anatomy of the Megaloxylon 

 stele may have been connected with the function of water- 

 storage 4 . 



The fern-like features in Lyginodendron are exhibited in the 

 structure of the stele of the petiole as in the form of the leaves ; 

 this resemblance to the ferns has led Prof. Zeiller 5 , while recognizing 

 the Cycadean features, to consider the genus as a member of the 

 Filicineae; but the striking affinities with Cycadean characters 

 revealed by the stem render the inclusion of Lyginodendron, 

 Heterangium and other genera in the class Cycadofilices, a matter 



1 Williamson and Scott (95), p. 767. 



2 Prantl (81), PL in. fig. 34. 



3 Haberlandt (96), p. 354. 



4 Since the above was written my attention has been drawn by Dr Scott to a 

 paper by Eothert in the current number of the Journal of the German Botanical 

 Society, in which parenchymatous tracheids with scattered bordered pits are described 

 as occurring singly or in groups in the pith of a species of Cephalotaxus. These 

 short tracheids are regarded as most probably water-reservoirs ; they bear a close 

 resemblance in shape and most probably in function to those of Megaloxylon, but 

 in the latter genus they form a considerable portion of the primary wood, while in 

 Cephalotaxus they appear to be modified elements of the pith. 



5 Zeiller (97), p. 198. 



