Page:Popular Science Monthly Volume 65.djvu/317

Rh, the Malay Peninsula and Java, indicated that the San Jose scale in eastern Asia can not survive below Shanghai.

The special district where it is native and thrives is a fairly well shut-off region, which probably accounts for the failure of this insect to become a world pest ages ago. This district is the region leading up to the mountains and comprising the northern and northeastern frontiers of China proper. Beyond the great wall on the north and west lies Mongolia, consisting chiefly of the vast Desert of Gobi. To the northeast and separating the region from Manchuria and Corea is

the eastern Gobi desert. To the south and east lies the great alluvial plain, the product of centuries of mud carried down by the Yellow River, a region where cereals only are grown. These are all effective barriers, and especially so when considered in connection with the political conditions of the past. We have, therefore, as the original home of this insect a naturally shut-off area from which it could not easily escape under the conditions prevailing up to our own times.

The means by which the San Jose scale came from China to America is a matter of interest. This pest reached California on trees imported by the late James Lick, a gentleman who was an enthusiastic