CYC ADAGES. 13 



the Mesozoic representatives of the same genus. The genus itself 

 is merely a provisional one, and rests on external characters of 

 vegetative structures, hut the cycadean habit is sufficiently obvious 

 to lend confidence to the generally accepted botanical position 

 assigned to this and other cy cad-like leaves. Portions of gigantic 

 leaves are figured by Renault and Zeiller from the Commentry 

 coal-field under the generic name Titanophyllum, 1 and it is 

 suggested that possibly these may belong to Calpoxylon stems, 

 which have been referred on anatomical grounds to the Cycadacece, 

 but these and many other leaf forms must remain in the list of 

 plantcc incerta sedis until additional facts are available. Eenault 

 has recently described another species of Permian cycad, Ptero- 

 phyllum Comlrayi? which shows a fairly close resemblance to 

 P. Jaegeri, Brong. Enough has been said to show that in Permo- 

 Carboniferous times there existed certain forms of leaf structures, 

 which must be assigned with the numerous Mesozoic fronds to the 

 provisional genera of extinct cycads. The large number of seeds 

 from this geological horizon, with their well-preserved structure 

 and variety of external form, are naturally a source of difficulty 

 as regards systematic position. There are distinct indications of 

 cycadean affinity in many of the silicified gymnospermous seeds ; 

 some belong, no doubt, to Cordaites, whilst others may be more 

 correctly placed in the Conifera. The seeds of the recent genus 

 Ginkgo show some points of contact with those of cycads, and 

 among the seeds of Palaeozoic plants it would not surprise us 

 to find cycadean and coniferous characteristics represented in. the 

 same species. We cannot well do more than speak of these doubtful 

 fossils as examples of Palaeozoic gymnospermous seeds, many of 

 which distinctly resemble the seeds of recent cycads. Grand'Eury 3 

 includes many such fossils in the family Noeggerattiacea, a sub- 

 section of gymnosperms ; the choice of this name is not a very 

 happy one, seeing that we know so little as to the actual position 

 of Sternberg's genus Noeggerathia. 



Ascending the geologic series from the Permian to the Upper 

 Jurassic strata, we find a gradual increase in the number and 

 variety of cycadean fronds, and in the Wealden vegetation the 



1 Renault and Zeiller, p. 622, pi. Ixix. 



2 (3), p. 672. 



3 (1), p. 301. 



