138 Rhodora Sr) 
readily see the sudden appearance of wind-spread plants, like the 
fringed-gentian, in spots where they have hitherto been unknown ; or, 
on our own St. John river, each spring we may see a wonderful wash- 
ing down of species from the upper valleys to the rich basin of Kenne- 
becasis Bay. The Indians, too, in their centuries of travel spread 
hundreds of species, long before we could take any account of them. 
Nevertheless, admitting such exceptions, we may fairly say that if the 
plant has not come to its present position through the direct or in- 
direct influence of historic man, dt is indigenous, otherwise itis intro- 
duced. 
How about the plants in question? It is well known, as we have 
already seen, that, in thickly settled regions of America, at least three 
of these plants are known to be of European origin; but so are many 
other species, yarrow, plantain, etc., which are likewise undoubtedly 
indigenous in the northern parts of our continent. And there are 
scores of species, common like the campion, mugwort, field sow-thistle, 
and hawkweed in northern Europe, which are certainly indigenous in 
America. Among these are the bog bilberry (Vaccinium uliginosum, 
the rock cranberry (V. Vitis-/daea), the yellow-rattle, (Rhinanthus) 
and the eyebright (Zuphrasia), all of which (excepting a few coast 
and mountain stations) have in the east the same southern limit of 
distribution as the plants which are especially under discussion. 
When, however, we look into their broad range in America, a sig- 
nificant fact appears. The yellow-rattle, for instance, grows in Labra- 
dor, Newfoundland, northern New Brunswick and Maine and in the 
White Mountains, on the New England coast, the northern shore of 
Lake Superior, in the Rocky Mountains, and thence north to Unalaska 
and the Arctic coast. Such in general is the range of all the plants 
which, coming from the north, reach in eastern America the same 
southern limit as the campion and its associates. The study of this 
peculiar distribution is one of the most important and fascinating 
problems for the northern botanist, but it must not now be allowed to 
take us far from the main subject. In this discussion we may accept 
without question the well-proved hypothesis that, prior to the glacial 
period, these plants were common in the circumpolar regions. As the 
glacial period came on the ice crept further and further equatorward 
and gradually drove all forms of life nearer the tropics. In time, 
when the ice-sheet covered New England, of course no plants could 
live here; but, as the ice melted away, those species which had 
