320 ANNUAL BEPORT SMITHSONIAN INSTITUTION, 1913. 



ical ancestry, as was first enunciated by Grisebach. They may be 

 distinguished from those of the ash by being alternately arranged 

 instead of opposite. There are numerous other details which enable 

 the student to distinguish between the leaves of the different genera 

 and species. It will be convenient to take up each genus separately 

 and describe something of its present range and such portion of its 

 geologic history as is Icnown. 



THE GENUS HICORIA. 



The hickories are now referred to the genus Hicoria, proposed 

 by Rafinesque in 1808, although many systematists, especially in the 

 Old World, still use the name Carya proposed by Nuttall in 1818 and 

 universally used until about 20 years ago. 



The hickories occupy a unique economic position, for while the 

 consum.ption of this wood is less in quantity than that of some of the 

 other hardwoods such as white oak or yellow poplar, or of various 

 coniferous trees like the cypress or the pines, it shares with the 

 black walnut the distinction of being the most costly American wood. 

 Hickory, while not remarkable for beauty of color or of grain, will 

 probably be the most difficult wood to replace when the approaching 

 shortage becomes more acute, since it combines weight, hardness, 

 stiffness, strength, and toughness to a degree unequaled among com- 

 mercial woods. The Forest Service estimates that the consumption 

 of hickory for lumber, spokes, tool handles, rims, shafts, sucker rods, 

 etc., amounted to 450,000,000 board feet during 1908, exclusive of 

 the large amount used as fuel, estimated at about 1,000,000 cords — 

 for hickory is also the best American fuel wood. 



The genus Hicoria is entirely confined to North America in the 

 existing flora, more particularly to the eastern United States, 

 although there is an indigenous species in Mexico {Hicoria mexi- 

 cana)^ and three or four other species reach their northern limit of 

 growth beyond the Great Lakes in eastern Canada. 



The existing species niunber from 8 to 15, according to the rank 

 assigned to the varieties of the 8 or 9 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 

 preglacial Pliocene times. 



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

 perate 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. 



