452 G. R. Wieland — Origin of Dicotyls. 



on the other hand Berry says that flowers are more plastic than 

 stem structures, which are " conservative." Pie sees no great 

 difficulty in the way of derivation of dicotyls from members of 

 the Williamsonian tribe or allied forms if the stems were not 

 in the way ! And as is well known, Arber and Parkin, Dr. 

 Scott, Professor Bessey, Hallier, and many others see no insu- 

 perable difficulty to dicotyl derivation from somewhere within 

 the Mesozoic cycad alliance either on the score of stem, leaves, 

 or flowers. 



Evidently the view of these latter eminent students comes 

 not only near to the true facts, but in the main represents the 

 consensus of botanical opinion as to the origin of the Angio- 

 sperms, so far as such opinion has taken definite form. 



But in any case, the question which seems hardest to answer 

 and which leaves the paleobotanists in a more " puzzle-headed " 

 position than any other is not the origin of either leaf or floral 

 or stem structures so much as how it is that the dicotyls ap- 

 peared so suddenly. The plant histologist may doubtless find 

 a means whether by way of Drimys or Gnetum of leaping the 

 hiatus of stem structure. He may too, depending somewhat 

 on temperament and knowing how strikingly few fossil flowers 

 have so far been found, conceive floral transformations and 

 reductions as relatively easy. 



Not so may we bridge the foliage hiatus just because instead 

 of scattered and isolated forms on which to base a general and 

 fairly accurate philosophic conception of the course of change 

 in stem and in floral structure leading up to Angiosperms, 

 there is a vast mass of representative leaf material from plant- 

 bearing terranes throughout the Mesozoic. And it all points 

 to a post-Wealden advance of comparatively modern types of 

 Angiosperms, seemingly from the north, and more sudden and 

 widespread than perhaps any other supplantation faunal or 

 floral throughout geologic history, — Une revolution, as Saporta 

 has said, ainsi rajpide dans sa marche qiCuniverselle dans ses 

 effets. 



Indeed we are brought face to face with the problem in 

 even severer aspect when a notoriously conservative botanist 

 like Seward emphasizes the general view that u the study of 

 the plant life of past ages tends to the conviction that too 

 much stress may be laid on the imperfection of the geological 

 record as a factor in the interpretation of paleontologicai 

 data." 



Accepting however, in the hope of reaching some result that 

 other students may be willing to accept, the hardest conditions 

 of solution in which the knotty problem of dicotyl origin may 

 be put, it is evident that some of the fairly obvious factors 

 have been left needlessly obscure. And several of these facts 



