THE AMERICAN BOTANIST 



75 



ern Europe and even extended to Greenland and Spitzbergen. 

 There are now no members of this group indigenous to Europe 

 and it is beHeved that all the European species perished during 

 the ice age. The walnuts, which are own cousins to the 

 hickories, were spread even farther, and extended from Alaska 

 across North America, Europe and Asia to Japan. This group 

 was more fortunate than the hickories and many escaped exter- 

 mination during the glacial period. Today representatives are 

 still found in Japan and the Mediterranean region as well as in 

 America. The walnuts and hickories seem never to have 

 spread very far into the tropics but the Jugiandaceae, the 

 family to which they belong, is represented there by several 

 small genera. In prehistoric times these spread north with 

 their allies even to Greenland but at present they are decidedly 

 tropical. Curiously enough, these tropical species lack the very 

 characteristic fruits of our species. Instead of hard-shelled 

 nuts, they have light winged fruits modified for distribution by 

 the wind. The tropical Jugiandaceae belong to the genera 

 Pterocarya, Platycarpa, Engelhardtla and Orconiunna. 



