294 EDMUND W. SINNOTT AND IRVING W. BAILEY 



woody plants in its flora. The advantages of the herbaceous habit 

 in a temperate climate are obvious. The plant is able to complete 

 its whole life-cycle during the summer season and to live through 

 the cold winter either under ground or in the form of seeds. Plants 

 which cannot resist cold are thus able to thrive in temperate 

 regions. It is a noteworthy fact that families whose members 

 have aerial stems which are generally able to withstand low tempera- 

 tures — such as the Fagaceae, Betulaceae, Salicaceae, Capri- 

 foliaceae, and, in fact, most of the woody families of temperate 

 regions — have few or no herbaceous species, for they have been 

 well able to get along without them. 



The gradual refrigeration of climate probably first dwarfed and 

 stunted the primitive arborescent vegetation, killing outright 

 many of the more delicate types, such as the fig, laurel, and cinna- 

 mon (of which we find fossil remains almost within the arctic circle) ; 

 and then, by continually killing back the whole year's growth of 

 these stunted shrubs, it probably converted them gradually into 

 perennial herbs. The annual herb, which starts from seed each 

 year, is evidently a still more recent development. 



The herbaceous type thus developed has usually proved very 

 vigorous and adaptable. It is far superior to the woody one in the 

 relative amount of seed which it produces; and the fact that its 

 life-cycle from seed to seed is completed in only one or two seasons, 

 rather than in the long period of years which is necessary with most 

 trees and shrubs, allows it to become dispersed much more rapidly. 

 Its abihty to live through adverse conditions of drought, in the 

 same way that it does through those of cold, gives it an advantage 

 in dry regions, and many herbs seem to have arisen in these dry 

 regions in adaptation to discontinuity in moisture alone. 



It seems most probable that herbs have evolved in the temperate 

 portions of the Southern Hemisphere and in mountainous, desert, 

 and even tropical habitats all over the world. The majority of the 

 important herbaceous genera, however, seem from their present 

 distribution to have originated in the temperate land mass of the 

 Northern Hemisphere. The ease of dispersal over wide areas and 

 the consequently keen competition among a great variety of plants 

 have resulted here in the development of an exceedingly hardy and 



