Before he attempts to formulate general laws, he must collect his facts, and examine them in detail. He goes out, perhaps, and gathers a flower: let us say the blue flax, Linum lewisii. The very name tells him something of its history; it was called lewisii in honor of Meriwether Lewis, of the famous Lewis and Clark expedition. It has been known since 1814, and has been collected by many botanists. Turning to the published records, it appears that it has been found as far south as the mountains of Mexico; as far north as Alaska. It does not occur in the eastern part of the continent, north or south. Among the native plants of America it has only one close ally, a smaller plant called Linum pratense—we may call it the prairie flax—which occupies open ground east of the Rocky Mountains from British America to Texas and again appears in Arizona.
In Europe and Siberia, however, there are closely similar plants; so like our Linum lewisii that for many years our plant was not separated. Furthermore, there are various other species of Linum or flax in the Old World, some of them strikingly different from ours. These, some with blue, some with red flowers, are more closely related to one another than to the yellow-flowered flaxes, which have lately been placed in a separate genus.
From all these facts, it is permissible to assume (in the absence of contrary evidence) that the genus Linum, in the restricted sense, belongs especially to and probably originated in the temperate regions of the Old World. This opinion is fortified by the discovery of a species (Linum oligocenicum Conw.) in European amber of Tertiary age. We imagine, then, the true flaxes originating perhaps in central Europe or Asia, segregating into various distinct species, and finally, perhaps during the Miocene period, invading North America. From the present distribution of the plant, we should naturally infer that it came by way of Bering Strait, not across the Atlantic; and from its slight divergence from the Old World stock we should think of it as a comparatively recent immigrant. The prairie flax, occupying a lesser area, and not so similar to the Old World type, is regarded as an offshoot from Lewis's flax, adapted to life on the prairies, the former occupying the mountains.
Leaving the flax for the moment, our naturalist hunts about and picks up a small shining cylindrical shell known as Cochlicopa lubrica. This snail is distributed widely over the continent, from Canada to Alabama, and west to the Pacific coast region. It is very constant in its characters, but in a few states has given rise to a variety or closely allied form of larger size called morseana. There are no other American allies.
So far, there is no apparent clue to its history; but when we turn to the eastern hemisphere we find a very different state of affairs. In the