18yr.] Botany. 147 
That a group of plants developed most abundantly in high northern 
latitudes should extend southward along north and south mountain 
ranges is precisely what one would expect, for in Such localities con- 
ditions resembling the normal would be obtained. Consequently a 
large number of distinctively boreal plants may be found on the tops 
of high tropical mountains, With this well-known fact of distribution 
in mind, it will be plain that one should expect a high mountain range 
to bring south a greater number of northern plants than could be 
brought by a low mountain range. Such a hypothesis would find 
some support, at least, if one considers the distribution of Canadian 
spermaphytic genera in the southwestern United States, and then in 
the southeastern. Of the two great mountain systems of North 
America, the western is much higher and extends farther to the south, 
Throughout Colorado the elevation of Rocky Mountain peaks is some- 
what over 13,000 feet, while the highest peak of the Alleghenies is 
barely 8,000 feet, above sea-level. The Rocky Mountain range from 
Montana to New Mexico averages about twice the height of the 
Appalachian chain frbm New York to the Carolinas. 
The accompanying table is compiled to exhibit what seems to be the 
clearly preponderant massing of typically northern: plants southwest 
rather than southeast. In the compilation only the more compendious 
lists have been employed. These are those of Macoun, Watson, 
Coulter, Chapman, Gray, and Porter. The table shows the number 
of species and varieties of several distinctively northern and south- 
bound genera in Canada, in the southern Colorado-and New Mexico 
regions, and in the southern Appalachian regions, respectively. For 
the most part, genera which have their greatest North American devel- 
opment in British America are the ones which have been selected. In 
the majority of cases, too, the genera chosen are those of wide range, 
east and west, in the Canadian region. It is possible that the figures 
are not exactly accurate for many of the entries, since only a little 
critical work on the nomenclature has been attempted, and some 
synonyms may have crept into the totals. Again, especially in the 
southwestern region, some entries should doubtless be made from the 
smaller plant lists, not given by the larger lists, which alone were €m- 
i ployed. This source of erròr, as will be seen, would not at all tend 
_ to vitiate the general results. 
