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THE POPULAR SCIENCE MONTHLY. 



Fia. 9.— Pecan ( Carya olivce/ormis). 



It is the presence in the hickories of staminate flowers in clusters of 

 threes, while in the walnuts there is but one ; and by the more or less 

 complete separation of the husks of the hickories into four pieces, 

 while the walnuts have no such division. 



Now, the pecan is allied to the walnuts by the number of its leaf- 

 lets (thirteen to fifteen, while the walnuts have, in one species, seven 



to eleven, and in others fifteen to twenty- 

 one), and by having its catkins separated at 

 the base instead of being united. And it 

 agrees with the hickories in having three 

 catkins instead of one, and by the husk of 

 the fruit separating into four pieces. The 

 kernel is very sweet, the husk is thin, and 

 the nut smooth and rather thin-shelled. The 

 peculiar feature of a bitter division between 

 the two halves of the nut is an approach 

 to those hickories having a bitter kernel : 

 while the hard shell and the sweet kernel 

 ally it to the shell-bark. The tree is con- 

 fined now to the States near or bordering the Mississippi River, and 

 is thus the nearest of all the species to that spot which was once thick- 

 ly clothed by its ancestors. It is noteworthy, too, that the walnuts 

 approach the same habitat, and in the case of one species extend across 

 the continent to California. 



From an aboriginal ancestor which probably possessed a many- 

 parted leaf, and a fruit with an entire husk and a thick shell, there 

 came two branches. One of these, retaining the numerous leaflets, 

 developed a nut with a corrugated shell and a thick, green husk, rep- 

 resented by the living species of walnuts. The other branch gave rise 

 to a species having a nut resembling the pecan, with a smooth shell, 

 and a husk separating more or less completely into four parts. Some 

 of the various stages of development from such an ancestor have prob- 

 ably been preserved to us. The white shell-bark may be regarded as 

 a modified descendant in which the bitter internal division has been 

 lost, and the outer shell strengthened to afford additional protection. 

 The mocker-nut and the thick shell-bark have acquired a still stronger 

 covering to protect them in the same way. The small-fruited hickory 

 is probably a stepping-stone to the pig-nut, with its thick shell and 

 partially bitter kernel ; while the thin-shelled bitter-nut and water 

 hickory are other offshoots in which the bitter kernel does away with 

 any necessity for a hard and thick shell. 



The geographical distribution of any species or genus is an in- 

 teresting and important adjunct to its history. At the present day, 

 all the species of hickories are natives of North America east of the 

 Rocky Mountains. Two out of four of the species of walnuts are con- 

 fined to the same limits ; a third is native to California and Mexico; 



