416 0, R. Wieland — Williamsonian Tribe. 



singular indeed, if persistent forms were not reported from 

 time to time, forms bearing the same simple longevous rela- 

 tion to an ancient and cosmopolitan race, as, for instance, the 

 New Zealand "Tuatara" bears to the Triassic Rhyncocephalia. 

 Accordingly, even after granting full validity of determina- 

 tion, no more than a casual interest can attach to the reported 

 occurrences of Triassic and mid-Mesozoic forms like JVilsSo- 

 nia in the Eocene, least of all in far northern regions long a 

 favored hypothetic home of early dicotyls. 



But, on the other hand, the fossil plant record is, we con- 

 tend, sufficiently well known to draw the main conclusions as 

 to culmination and extinction in the case of a large and cos- 

 mopolitan group like these cycads. Nor is there anything in 

 all the paleontologic record more impressive than the manner 

 in which, following the steady disappearance of seed fern ,and 

 Medullosan types, the Williamsonian alliance quickly spread 

 over the earth and then " disappeared " before the invasion of 

 the Angiosperms. 



With a few further remarks on what is conceived to be the 

 older type of Cycadophytean leaf and its possible variation in 

 the direction of net-veined leaves, we shall be ready to show 

 the range of fructification so far determined in the William- 

 sonias. 



There is excellent reason for saying that the most ancient 

 type of Cycadophytean leaf was of more or less Marattiaceous 

 aspect. At least Cycadotilicalean foliage is of this general 

 appearance ; though ultimate relationship to other gymno- 

 sperms, especially the Cordaitales, and eventually even to 

 Angiosperms, must also have found clear expression in the 

 foliage of the later Paleozoic. However, a possible transition 

 from these earlier members of the ancestral line in the direc- 

 tion of Pterophyllum and Wielandiella is suggested by old 

 bladed types like Oleandra, Oleandridium, and perhaps early 

 Nilssonias — that is, if outward and general form only are had 

 in mind. For while on the one hand the Tseniopterid series 

 approaches very near to Nilssonia, the latter may on the other 

 include quite diverse elements. 



But while as we see the Cycad leaf type was fully differ- 

 entiated even in the Permian and earlier, and reached variety 

 within its somewhat stereotyped limits in the Trias, the rela- 

 tion of leaf genera to chronology has not been worked out with 

 sufficient exactness to serve in Mesozoic stratigraphy, save in 

 the most general manner. In fact, we have confronting us a 

 great plexus of leaves exhibiting every gradation from laminar 

 to pinnate and bipinnate forms, with venation varying from 

 parallel through the commoner dichotomous to long and finally 



