30 



they are large and long. This is particularly the case In the Dldy- 

 mocarpi and Leptocarpi and has led to the founding of spurious 

 species on this character. 



No fossil species of Astragalus have been certainly reported, 

 while the geographical distribution points clearly to the Glacial period 

 as the beginning of the primitive species. 



Doubtless there will always be discussion as to the indigenous or 

 foreign origin of some species bHt generally speaking there is no 

 reason to seek a foreign origin for any not known to be continental. 

 Those species which are now contiguous in the Arctic, the Alpini, are 

 of European or Asiatic origin, as well as the Hypoglottides, and prob- 

 ably the Uliginosi. But the Hamosi of America though closely re- 

 sembling those of Europe show no common origin with them but 

 come down through the Flexuosi, or A. nitidus, and from the Hamosi 

 come the rest, such as the Leptocarpi, Micranthi and Didymocarpl, 

 though the latter may have come from the Hypoglottides. If the 

 line of descent were not clear then we might be j'JStified in seeking 

 a foreign origin, but though there are abnormalities and gaps yet as 

 a whole the line of descent of all the species is well marked. While 

 to connect our anomalies with species of remote regions in Europe or 

 Asia would require far more unscientific guessing and stretchin.^ 

 of ecological laws than the facts warrant. For example A. succum- 

 bens has no near relative and yet its relation to the Hamosi is 

 evident as well as with the Galegiformes. The Uliginosi are evidently 

 of common origin with A. nitidus and presage the Preussii. The 

 higher groups the Leptocarpi, Micranthi and Didymocarpl are the 

 most differentiated and both ecologically and geologically have been 

 subjected to the most changes of climate and the greatest migration, 

 as shown by their present distribution and annual habit. We have 

 hardly a suspicion of the spinose Astragali of Asia. A. jejunus 

 and humillimus have rigid petioles as well as A. sesquiflorus, but 

 never spinose. The adaptation of the species to climatic conditions 

 is perfect as is that to soil whether the soil contains 1 per cein of 

 soluble alkalies, or is acid as in the alpine meadows, or is barren 

 clay as in the Navajo Basin, or the gravelly plains of Colorado and 

 Montana, or the cooking-hot deserts of Arizona and Mexico. There 

 is no evidence of present progressive differentiation, not even in 

 such a cosmopolitan and variable species as A. lentiginosus. There 

 is little hybridization and little evidence of fertility of hybrids. The 

 species are easily definable though some are variable. The limits 

 of a few species are uncertain, particularly Mexican, from lack of 

 information. In fact many of the newer Mexican species are merely 

 tentative, for there are at least a score still to be discovered which 

 are liable to alter our conception of the limitations of the Strigulosi 

 and Micranthi. 



LIFE ZONES. 



The prime factors in determining life zones are humidity (which 

 Includes that of the air and soil), temperature, soil, and light. Since 

 the light is a matter of exposure, it varies locally, the same is true 

 of the soil. Humidity is at the basis of all plant growth and should 

 form the basis of all classification but unfortunately it varies with 

 altitude, exposure, drainage and many other things and so Tem- 

 perature is alone left to govern our plant zones. This varies with 

 altitude and latitude. We first find what are the actual plant zones 



