GEOLOGIC HISTORY OF THE LOCUST 

 ' AND ITS ALLIES 



EDWARD W. BERRY 



The Johns Hopkins University, Baltimore, Maryland 



A consideration of the locust ^ and its allies introduces us to 

 one of the largest alliances of flowering plants, popularly kno^\Ti 

 as the Leguminos2e, and now divided by botanists into four 

 families. These are the acacia or mimosa family (Munosaceae), 

 the senna family (Caesalpiniacese), the krameria family (Kra- 

 meriacese), and the pea or bean family (Papilionacese) . Among 

 these there is a well marked floral progression from the first, 

 with its regular flowers, to the last, with its butterfly-like blos- 

 soms. The first two families are very old geologically and are 

 largely arborescent fonns of the tropical zone, many species of 

 which have been found fossil in the Tertiary deposits of our 

 southern states. The last two families, on the other hand, are 

 mainly herbaceous fonns dwelling outside the tropics, and both 

 have probably attained their maximum of variation in the 

 Temperate Zone since the inauguration of the Pleistocene 

 glaciation. 



A large number of leguminous plants furnish most important 

 food or forage crops (Pea, bean, lentil, peanut, tamarind, 

 alfalfa, clover, etc.) or are utilized in medicine (senna, licorice, 

 etc.) or other arts (indigo, logwood, gum tragacanth, gum 

 arable, copaiba gum, etc.). The habit of many of the Legumi- 

 nosae of abstracting nitrogen from the air by means of root 

 bacteria makes them of especial interest in these days of the 

 rapid exhaustion of natural nitrates. Many tropical Legumi- 

 nosse are important timber trees (brazil wood, iron wood, violet 

 wood, etc.) but outside of local uses the world's markets know 



1 This is not the locust tree of southern Europe, which is the carob, Ceratonia 

 siliqiia, a member of the Caesalpiniaceae. 



284 



