454 



G. B. Wieland — Origin of Dicotyls. 



the gradual growing forward of the basal wings along the mid- 

 rib with adoption of the netted venation and suppression of 

 the apical pinnules. The varied transformations in leaves as 

 seen for instance in Orchids do not permit such a method of 

 derivation to remain an unnoted possibility, but there being no 

 evidence that the basal wing advanced beyond the condition 

 seen in Wielandiella. it is necessary to further consider the 

 method of origin by fusion of pinnules. 



The venation, and especially the size and form of Dryophyl- 

 lum and Ziriodendropsis, to cite definite generic examples of 



Fig. 1. 



Fig. 2. 



Fig. 1. Pterophyllum fissum Fstm. 

 x 1/1. Abundant in shaly beds near 

 Burio, Kajmahal Hills. After Feist- 

 mantel. 



Fig. 2. Cycadeoidea ingens(type). 

 Freehand drawing of young stoni- 

 ata showing their somewhat fern- 

 like and generalized character. The 

 form appears somewhat nearer to 

 that of Dicotyls than does that seen 

 in existing cycads. 



Cretaceous dicotyls, do lend some plausibility to the idea of 

 direct derivation from cycad fronds, more especially Pterophyl- 

 lum. And according to the view of Arber and Parkin* a 

 cycad ean type of foliage was probably long retained in a simple 

 stemmed angiosperm ancestry, while concomitantly with 

 development of the branch habit these early megaphyllous 

 forms finally acquired netted veined microphyllous foliage, the 

 so-called " sudden appearance " of the angiosperms in Neoco- 

 mian times, thus being the simple resultant of rapid transition 

 in an already highly evolved and " diversified " group. 



* The Origin of Angiosperms. Linn. Soc's. Journal — Botany, Vol. xxxviii, 

 p. 69, July, 1907. 



