552 THE POPULAR SCIENCE MONTHLY 



Michigan, 3 southward in the eastern part of its range to Delaware, and 

 in the west to southeastern Indiana 2 and extreme southern Illinois, 4 

 while it extends along the southern Appalachians to north central Geor- 

 gia, 5 central Alabama 6 and Mississippi, and central Tennessee. This 

 distribution is most easily remembered if we observe that it takes the 

 general form of an ellipse, which is about twice as long as broad, with the 

 southern end in central Mississippi, Alabama and Georgia, the northern 

 end in Maine, Xew Hampshire and Vermont, while the greatest cross 

 diameter of the ellipse extends from southeastern Michigan to Delaware 

 (Fig. 1). 



Although this is the area which now includes all chestnut growing 

 naturally or "wild" in the United States, it does not necessarily repre- 

 sent the territory it has always occupied in the past. For geological evi- 

 dence, as well as our own observational powers, show us that in both 

 plant and animal worlds the confines of a species are constantly varying 

 — now expanding, now contracting. This condition is evidently due to a 

 great variety of factors, but at the very groundwork of them all lie the 

 fundamental principles of the struggle for existence and the survival of 

 the fittest. In modern times the modifying action of man on this per- 

 petual contraction or expansion of a species has been by no means slight, 

 and with the ever-increasing facilities of commerce, his influence is be- 

 coming more and more marked. To cite an example from the plant 

 world, some of the most obnoxious weeds that grow about us to-day, and 

 are the bane of the farmer, are intruders from foreign countries, their 

 seeds having been brought in with various imported materials. Having 

 thus arrived here, many of them find congenial soil and make their home 

 among us, thereby considerably widening the range of distribution of 

 their particular species. On the other hand, by the unwitting introduc- 

 tion of various fungous or insect parasites, man may be instrumental in 

 the contraction or even the extinction of some of our plant or animal 

 species. 



Such examples as the bison, or the Xorth American Indian, demon- 

 strate how rapidly the distribution of a species or race may change, even 

 within the memory of man. 



Geological data, as furnished us in the form of fossils, are often illu- 

 minating as to the former distribution of our plant and animal species. 

 For example, the giant big-tree and redwood, of California, quite prob- 



3 Otis, C. H., and Burns, G. P., "Michigan Trees, a Handbook of the Native 

 and Most Important Introduced Species," p. 95, Ann Arbor, 1913. 



4 Gleason, H. A., "Additional Notes on Southern Illinois Plants," Torreya, 

 4: 168, 1904. 



5 Harper, K. M., "Flora of Middle Georgia," Bull. Torrey Bot. Club, 27: 

 333, 1900. "Botanical Explorations in Georgia During the Summer of 1901," 

 ibid., 30: 294: 1903. 



eMohr, Charles, "Plant Life of Alabama," Contributions from the U. S. 

 Nat. Herbarium, 6: 60, 1901. 



