NOTES ON THE GEOLOGICAL HISTORY OF THE WAL- 

 NUTS AND HICKORIES 



EDWARD W. BERRY 



The Johns Hopkins University, Baltimore, Maryland 



The walnut family ( Juglandaceae) , which in the popular mind 

 is fully rounded out by the enumeration of the walnut, butter- 

 nut, hickory and pignut, while relatively small, is by no means 

 as limited as this might indicate. According to current inter- 

 pretations there are six genera and about 'forty species widely 

 scattered throughout the warmer parts of the north temperate 

 zone and penetrating some distance south of the equator along 

 the Andes in South America, and in the East Indies. 



The Juglandaceae are of considerable interest for a variety of 

 reasons, chief among which, aside from their great economic 

 importance, are their long line of ancestors reaching back some 

 millions of years to the Mid-Cretaceous, and the former wide 

 range and abundance of these ancestors, which also serves to 

 explain the curious geographical distribution of the still existing 

 species. They are also interesting because of the much discussed 

 question as to whether their morphological characters shall be 

 interpreted as primitive or as mere simplifications of a more 

 highly organized stock. 



Not all of the genera have adopted the same methods of seed 

 dispersal and certain genera have kept the seed part of their 

 fruits comparatively small and light, thus enabling them to 

 produce large numbers of seeds with the same expenditure of 

 energy required for a single walnut. Furthermore, instead of 

 depending altogether upon chance for the dissemination of their 

 latent progeny, the bracts which are normally present have 

 developed enormously and serve as wings. This is especially 

 true in the genera Engelhardtia and Oreomunnea and will be 

 referred to on a subsequent page. 



225 



THE PLANT WORLD, VOL. 15, NO. 10, OCTOBER, 1912 



