36 
aate the former flora of the Sopor of the two basins from the present 
except by the present isolation of species. The distribution of A. ci- 
barins and Shortianus would indicate an early origin. The wide and 
almost cosmopolitan distribution of A. lentiginosus would point to a 
very early origin but this is only apparent as the nature of the pods 
is such that wind transportation is sufficient to’ account for it, while 
all its affinities and ite development would indicate an origin much 
later in the Lower Temperate from which it has spread to the Middle 
Temperate... There are many instances of similar invasions by other 
species. -A. Hookerianus now grows freely in the Middle Temperate 
life zone though its home was in the spruce zone. The same is true of 
A, aboriginum, a plant now normally of the Middle Temperate which 
came. from the spruce zone. The Astragaline flora of the gresi. 
Plains region to the: Atlantic is of little interest, the climate being 
that of latitude only, presenting none of the divisions so marked in the 
Great Plateau due to barriers of mountains and arid plains and great 
differences in humidity, as well as soil conditions. There is nothing 
in the flora to indicate ancient origin of the few new formis. A. neg- 
lectus may have been an offshoot of Canadensis, early or late. A. 
Plattensis and Tennesseensis are manifestly late modifications of the 
Sarcocarpi. A. distortus and glaber are evidently products of a 
hotter climate than the Middle‘ Temperate and probably are related 
to the. Hamosi.. This region alone furnishes abundant evidences that 
the so much vaunted struggle for existence by crowding is a myth. 
Astragalus is a genus of sunlight and open air; a: genus of hills and 
exposed rocks, meadows, prairies, plains and drifting sands, . Crowd- 
ing alters its habits but not its species... It is a genus essentially of 
. the sodless regions of the west. ^ =; 
. - The disappearance of the continental ice sheet was clearly caused 
by elevation of the Arctic lands shutting off the water at the north 
and by a change in the Ocean currents of the Pacific.. This at the same 
time shut off the moisture from the Great Basin and the Columbia 
region, but the latter lake was drained by erosion as well, following 
the close of the Ice age, the Great Basin was not, but was a clear 
case of advancing aridity. "The disappearance of such vast bodies 
of water as that of the Columbia Lake and the two great lakes La- 
hontan and Bonneville, each about 18,000 sq. miles would have a 
profound effect on the climate, and at last ceased to have an appre- 
ciable effect in increasing the natural humidity of the region. This 
necessitated the extinction of the Middle Temperate flora from the 
floor of the Great Basin and the invasion from the south. of the Lower 
Temperate. This resulted in the replacement of the spruce flora of 
all the region north of Utah by the Middle Temperate nearly as far 
as the Canadian line, and the extinction of. the Middle Temperate 
flora throughout. the Great. Basin, some of the Columbia Basin, and 
the Navajo Basin as to the floor of those basins: This formed many 
isolated regions in the mountains of the Great Basin, and caused 
the flora to disappear on all the lower mountain ranges in the Basin 
at the south and in New Mexico, Arizona, Mexico and California. 
Our knowledge of the floral migrations of Mexico is meager, but we 
know that.the Middle Temperate flora has. entirely disappeared ex- 
cept in isolated places in the Sierra Madre plateau, and on the volca- 
noes of central Mexico and southward at high elevations. The 
true Upper Temperate flora never seems to have existed in Mexico at 
all since. what there is is clearly a modification of the Middle Temperate 
Now in Mexico not only the Middle Temperate has been replaced by 
the Lower Temperate but even this has for the most part given way 
to the arid Tropical except on higher ranges and peaks. . Geological 
evidence is clear that this pericd of aridity has been at least 10,000 
years old since the erosion of the old Bonneville beaches would in- 
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