Page:Popular Science Monthly Volume 84.djvu/557

Rh had formerly a much wider range than their present contracted limits, for fossils of conifers belonging to the same genus have been found even as far north as Greenland. And it is reasonable to assume that, if conditions remain the same, such species will continue to weaken and die out, although in this case also man's treatment can considerably modify the result.

Unfortunately, in the ease of the American chestnut, there is no fossil evidence of its former distribution. Mr. F. H. Knowlton, of the United States Geological Survey, writes us: "So far as I know, the American chestnut has not been found fossil anywhere in this country, but the parent form, that of Castanea sativa (the European chestnut)

 The cross hatching shows in a general way the extent of territory covered by the chestnut bark disease.

has been found at a number of localities in England and Italy, in deposits of inter-glacial or pleistocene age." As far as the genus is concerned, Castanea once had a much wider range in North America than at present, for, according to Sargent, "Before the middle tertiary period Castanea existed in northern Greenland, and in Alaska, where traces of the leaves and fruit of Castanea Ungeri Heer have been distinguished;