tg EN EE TAE E aoe ees | ae Ue Ss Say 
Na eT 4 ee eS u ome iy (Ae SS oe i áj 
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NATURAL HISTORY OF THE VALLEY OF QUITO. 655 
mountains, ascending higher and higher as the cold receded, till 
they found an asylum at the altitude where the climate. corre- 
sponded with that of the latitude of their native home. As the tide 
leaves its drift in horizontal lines, so would the living waters leave 
their living drift in isothermal lines on the mountains of the 
equator. 
If, then, a vast glacier covered North America from the Pacific 
to the Atlantic, and from the Pole,to the Ohio River, or still more 
southerly, the depression of temperature would be sufficient to. 
allow some temperate plants to sojourn in the Isthmus, and even 
to reach the equator. We should, therefore, look with some con- 
fidence for some remnants of our flora on the highlands of New 
Granada and Ecuador, or at least for some allied and representative 
forms. There would, of course, be some stragglers from the south : 
but, as Hooker has remarked, many more plants have migrated 
from the north to the south, than in a reversed direction. We 
have excellent evidence, says Darwin, that the glacial epoch was 
an enormous age, so that there was time enough for such a migra- 
tion. Doubtless, there was time also for modification, and some 
of these wanderers might exist in their new habitat, as new vari- 
eties, or even distinct species. Still they would be plainly related 
to their brethren of the Temperate Zone. 
The climate of North America 36° 30’ and northward cor- 
responds to the climate of the equatorial Andes at the altitude of 
eight thousand feet and upwards. The intervening land of Cen- 
tral America is too low and tropical to allow the passage of tem- 
perate plants by ordinary migration. But if this region was 
turned into a temperate zone in the glacial epoch, the chasm is 
bridged. Comparing the exogenous flora of the Valley of Quito 
with that of our Northern States east of the Rocky Mountains and 
eliminating those species which occur in both localities, but are 
indigenous to neither, such as chickweed (Stellaria media), straw- 
berry (Fragaria vesca), goose grass (Galium aparine), mudwort 
(Limosella tenuifolia), black night-shade (Solanum nigrum), pansy 
iola tricolor), and peppermint (Mentha piperita), we find the fol- 
lowing which are. native to the United States, and also pomar at 
Quito :— ( 1) The bellwort (Specularia perfoliata). This isa tem- 
Perate plant, and would not be likely to endure the transit of the 
tropics as they now are:. We may suppose it was intentionally 
introduced by the Quitonians, but this is not probable, as it 1s not 
