G. R. Wieland — Origin of Dicotyls. 457 



forms with one basal ear (PtilophyllumJ, two basal ears {Otoza- 

 mites) and finally modern and specialized cycad pinnule types. 

 It is indeed a striking fact that the more generalized types are 

 the older, and equally interesting to find that, as I have 

 proven, it is exactly in the lowermost Liassic that transition 

 types of pinnules are very abundant (fig. 3).* While too it 

 mast never be forgotten what rarities fossil flowers really are, 

 and what a botanic incognito with endless possibilities of 

 primitive relationships to the Angiosperms is involved in the 

 mere mention of the forms just now cited. 



Nevertheless, this first hand point of view of transition 

 from Cycadophytes already known must be left in abeyance, 

 not because it is unthinkable, and not because it is in itself 

 regarded as inherently impossible or unlikely, but just 

 because there is such an astonishing lack of evidence for 

 it, such an extraordinary absence of adumbrant forms, while in 

 the existent flora there is a group of plants which would un- 

 doubtedly be classed as a possible Angiosperm precursor 

 were it definitely recognized in Liassic or later deposits. 

 I refer to the G-netales, Welwitschia, etc. These, however, 

 lack a fossil record almost entirely while in strong contrast 

 the characteristic old cycadophytan types are the Pterophyl- 

 lums ; and though the latter are cosmopolitan all through Meso- 

 zoic time, nowhere do they show traces of net venation, the last 

 members of the group being as devoid of such traces as the first. 

 Indeed the Wealden cycads still include Pterophyllums which 

 are on the whole even more strictly and fixedly cycadophytan 

 in their general appearance and structure than the Triassic 

 forms. The cycadophytan race in short appears as time goes 

 on to rigidly fix its leaf characters, to even become senile, 

 rather than to exhibit hypothetic transition types toward net 

 venation. The isolation of Stangeria with slight marginal 

 venation doubly proves this tendency to fixity. 



.Nor can we on last analysis consider Dictyozamites in itself 

 an adumbrant form. It is not only specialized and exceptional, 

 but distinctly cycadaceous in form to a degree emphasizing 

 even more sharply the absence all over the globe from 

 Triassic to Wealden time of transition forms pointing towards 

 dicotyledonous leaf types. But what the Indian Dictyozamites 

 and the accentuated form of pinnule border-netting seen in 

 Stangeria do suggest, I contend, is the fundamentally 



* The leaf shown in figure 3 is from horizon 19 of the Rio Consuelo section. 

 See my paper on the Liassic Flora of the Mixteca Alta, etc. in this Journal 

 for Sept. 1913. This is an abundant and interesting type, and could quite as 

 well be placed in the the genus Pterophyllum as Otozamites. The further 

 interesting feature commented on in the text is that the obovate form is com- 

 mon to many species and varieties of Liassic cycads of virtually microphyl- 

 lous habit. 



