228 EDWARD W. BERRY 



The existing species number from eight to fifteen, according 

 to the rank assigned to the varieties of the eight or nine easily 

 distinguished and main types. They fall naturally into two 

 groups — the true hickories and the pecan hickories — groups which 

 were already clearly defined in pre-glacial Pliocene times. 



The true hickories are fine, slow growing trees of in general 

 temperate dry soils with hard strong wood. The buds are full, 

 with overlapping scales, and the nuts are generally thick shelled 

 and thick husked, while the leaflets are from three to nine in 

 number. The pecan hickories are trees which require warmth 

 and moisture, and possess relatively weak wood. The buds are 

 thin and narrow without overlapping scales and the nuts have 

 thin shells and thin husks while the leaflets are numerous, slender, 

 and falcate. 



Over a score of fossil species have been described. Unlike the 

 walnut the hickory is not known with certainty from the Cre- 

 taceous, but it is present in every early Eocene deposits in Wyo- 

 ming and on the Pacific coast. Hickories occur in the upper 

 Eocene of Central Europe and there is a fine large leafed species 

 from deposits of this age at Kukak Bay, Alaska. The Oliogocene 

 occurrences are largely referred to Hicoria ventricosa which is 

 abundantly represented by leaves and fruit in the Oliogocene 

 browncoal deposits of Europe. The late Miocene appears to have 

 been the period of widest extent of the hickories. From deposits 

 of this age about a dozen species are known. Trees were scat- 

 tered all over Europe and the genus extended to Iceland, Green- 

 land and Spitzbergen. In North America there were species in 

 Oregon and California, in Colorado and in Vermont. A species 

 very close to the existing pecan occurs in the late Miocene of 

 New Jersey. 



During the succeeding Pliocene period the hickories are as 

 abundant and vigorous as in the late Miocene in Europe although 

 their northern limit appears to have become somewhat restricted. 

 Even as late as the Upper Pliocene several species of hickory 

 are abundant in Italy and Germany but none survived the Ice 

 Age on that continent. 



A species resembling the pecan is represented by both leaves 



