458 G. R. Wieland — Origin of Dicotyls. 



important fact, that the Williamsonian tribe must have included 

 still other net-veined types which led directly into the Angio- 

 sperms. Although by reason of their entire nature and 

 structure the Mesozoic examples of these true dicotyl ances- 

 tors would indubitably find place in the same section of the 

 Cycadophytans as the known and typical Williamsoniaus. 

 What further relationship such hypothetical forms had to 

 the ancestral Gnetaleans can of course only be answered as 

 discovery goes on. 



But considering only the broader fact that these intermediate 

 ancestral types have so long remained inscrutable, where was 

 their home ? In the Arctic and Antarctic areas of course. This 

 is the inevitable conclusion to which the negative evidence 

 must lead. For we are bound to assume the Angiosperm 

 ancestry was wide in occurrence and widely related to other 

 groups. It is indeed very difficult to believe that any of the 

 dominant plant types have had sudden or confined origins. 



Theoretically it is, as already noted, fairly easy to assume 

 transitions from cycad to dicotyledonous leaves. But that 

 transition, as already noted, does not appear to have passed 

 from known forms. I repeat, in India, in Turkestan, in 

 North America, all over Europe, the absence of precursor and 

 adumbrant net-veined forms suggestive enough in character or 

 impressive of number, is so universal that it is safe to say 

 from the facts of known distribution alone that such mainly 

 originated in the peculiar climatic conditions of the Polar 

 areas, and there developed that invasive power which so sud- 

 denly transformed the forest facies of the globe in post- 

 Wealden time. 



The idea of extensive northern origins of dicotyls is how- 

 ever far from new. It has been canvassed by many botanists 

 from the time of Forbes and Darwin. It was given specu- 

 lative form by Saporta ; while Nathorst and Gray showed an 

 extensive Tertiary movement of plants from the Arctic. 



Earlier than any of the above the learned Riitimeyer, in his 

 famous essay of 1867 " Ueber die Herkunft unsere Thierwelt, " 

 recognized clearly enough that an Arctic and Antarctic conti- 

 nent had played a great role in present and past distribu- 

 tion ; while Haacke's subsequent paper on the north pole as 

 the great " Schopfungscentrum " of the Mammalia is, in view 

 of the intervening work of Wallace, simply a recessional view 

 rather than a step forward. Later Wortman considered the 

 extensive parallelism of the fossil mammalian fauna of Europe 

 and America pointing to Arctic origin ; and in the same year 

 (this Journal, December 1903) the present writer examined the 

 general subject, probably for the first time extending on a suffi- 

 ciently broad geophysical basis the original bipolar view which 



