130 TRANSACTIONS, NATURAL IirSTORY SOCIETY OF GLASGOW. 



•' Sur la valeur du genre Trizygia" to the Soc. Geol. de France, 

 in which he advocates the union of Trizygia and Sphenophyllutm. 

 He cites several cases where well-known species of Sphenovhyllum 

 have been known to show an inequality in the size of the leaves 

 forming the whorl, and simulating in this respect the charac- 

 teristics of Trizygia." 



It must be noted, however, that in Trizygia the inequality in 

 the size of the leaves in the whorl is a constant character, but in 

 Sphenophyllum it is an accidental occurrence. 



Seward in his Fossil Plants unites these two genera,^ but 

 this course I do not feel inclined to adopt, and prefer to leave 

 the question open for the present. 



Sphenophyllum, not only in the structure of its stem, but also 

 in that of its cones, exhibits so many peculiarities that it is im- 

 possible to class it with any other group of plants. With the 

 Calamites it has a certain superficial resemblance in the ribbed 

 stem and whorled leaves, but the solid axis, the non-alternating 

 ribs of Sphenophyllum, its dichotomous division of the segments 

 and veins of the leaves, and also the structui'e of its cone, dilfer 

 so much from those of the Calamites that any systematic re- 

 lationship is entirely precluded. With Archceocalamites (Bornia) 

 it has a greater resemblance in the ribs of Archceocalamites not 

 alternating at the nodes and in the leaves being dichotomously 

 divided, but it differs here also in its solid axis^ and in the 

 structure of the cone (presuming that Pothocites is the fructifica- 

 tion of Archceocalamites).^ 



With the Lycopodiacece also, Sphenop)hyllum, seems to have no 

 close connection. When describing the fructification of Spheno- 

 phyllum trichom,atosum, Stur, in 1891, my belief was that 



1 Bull., 3^ S4r., Vol. XIX., p. 673. 1891. 



- For reference to these figures, see Zeiller's paper, I.e. 



'Seward, Fossil Plants, Vol. I., p. 411. 



* For structure of Archcuocalamites Gopperti, see Solms-Laubach, Uher 

 die in den Kalhsteinen des cidm von Glutzisch Falkenherrj m Schlesien 

 erhaltenen strtictur hietenden Pflanzenreste. Botanisches Ztitung, 1897, 

 Heft. XII., p. 219, PI. VII. 



° Kidston, " On the Affinities of the genus Pothocites,"' Paterson. Ann. 

 and Mag. Nat. Hist., Ser. 5, Vol. XL, p. 297, Pis. IX., X., XL, figs. 9-10 ; 

 XIL, figs. 13-16, 1883; ibid., Proc. Roy. Phys. Sac. Edin., Vol. XVL, 

 Pis. I., XL, III., figs. 9-10; IV., tigs. 13-17 



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