G. It. Wieland — Origin of Dicotyls. 451 



Art. XXXVIII. — Was the Pterophyllum Foliage Trans- 

 formed into the Leafy Blades of Dicotyls f by Gr. R. 

 Wieland. 



The Angiospermous mode of sporophyll emplacement in the 

 form of a compacted bisporangiate fruit-producing branch of 

 limited growth, or "flower" with its perianth, was, so far as 

 the paleontologic record has as yet disclosed, first evolved in 

 Permo-Triassic time. Omitting any discussion of the catkins 

 of Cordaites, the oldest example yet recovered characterizes 

 Wielandiella from the uppermost Trias or Rhat. But the 

 fruit of this slender stemmed, rather freely branching plant is 

 of even smaller size than in existing Magnolias, and shows 

 rather more staminate reduction than any of its mid-Mesozoic 

 Williamsonian relatives; while the foliage may even be of 

 very old type, the leaf taken by itself being difficult to separate 

 from the fern Tceniopteris. However it is only a few years 

 since this ancient flower was first discovered and on recalling 

 the similar rare occurrence of typical Angiospermous fossi] 

 flowers inferential]} 7 abundant throughout most of Cretaceous 

 time, it becomes evident enough that the apparent absence of 

 Cycadophytan flowers in the collections from the early Triassic 

 has little significance. 



Following this scantily recorded advent and the worldwide 

 dispersion of the Cycadaceous bisporangiate strobilus or bi- 

 sexual flower as it may equally well be called, the next great 

 event in Mesozoic plant-history was the displacement of 

 dominant macrophyllous cycadaceous leaf types by the micro- 

 phyllous bladed net-veined leaf of the post-Wealden forest 

 facies. How absolute and complete this change was any one 

 may vividly realize for himself by recalling merely the outlines 

 of the paleontologic record as he walks through any present- 

 day forest, tropic or temperate. And any one who is willing 

 to either leave in abeyance the Monocotyls or to very reason- 

 ably suspect them to be a secondary or early lateral offshoot 

 from the main dicotyl stem, may thus simply vizualize the net 

 result of plant development in the Mesozoic, since the signi- 

 ficance of conifer culmination in the Lower Cretaceous appears 

 to be mainly ecologic. But how was the great transition from 

 a dominant forest of dichotomously-veined cycadophytan leaf 

 types over into net-veined blades actually accomplished ? 



Seward has recently stated that stem structures offer no dif- 

 ficulty in hypothesizing the descent of dicotyls from gymno- 

 spermous types. In fact the magnoliaceous genus Drimys has 

 as simple stem structure as conifers, which in part are of course 

 near to cycad stems, especially some of the older ones. While 



Am. Jour. Sci.— Fourth Series, Vol. XXX VIII, No. 227.— November, 1914. 

 31 



