36 



M.rite the former flora of the f^oor of the two basins frc-ni the present 

 except by the present isolation of species. The distribution of A. ci- 

 barius and Shortianus would indicate an early origin. The wide and 

 p.lrrost cosmopolitan distribution of A. lentiginosus would point to .1 

 very onr)''- origin but this is only apparent as the nature of the pods 

 is sich that wind transportation is sufficient to account for it, while 

 all its affinities and its development would indicate an ori9;in 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 grerl 

 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 forms. A. neg- 

 leotus 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 Ix)wer 

 Temperate. This resulted in the replacement of the spruce flora of 

 all the region north of Utah by the Middle Tempernte nearly as far 

 as the Canadian line, and the extinction of the Middle Temperate 

 flora throughout the Great Basin, sr-me of the Colmbia 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, bnt 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 period of aridity has been at least 10,000 

 years old since the erosion of the old Bonneville beaches would in- 



