No. 543] NOTES AND LITERATURE 



167 



ter, including many tables, temperature, rainfall, etc. From 

 the eternal ice and snow of Greenland to the equatorial condi- 

 tions on the Isthmus of Panama, practically the whole gamut 

 of climate depending upon latitude is covered. Moreover, the 

 great variety in topography in North America results in pre- 

 cipitations ranging from practically nothing in the extreme 

 deserts of the arid southwestern United States and Mexico, to a 

 rainfall of two hundred inches or more in some tropical rvu'ions 

 like parts of Jamaica. 



The presence of lofty mountains permitting a rich Alpine flora 

 in the northwestern parts of the United States and Canada, is 

 also an interesting feature of the vegetation of North America. 

 In his division of the phytogeographical regions Ilarshberger 

 recognizes four main divisions : Northern, Central, Southern and 

 West Indian. The United States lies almost entirely within the 

 second of these, only the region of the Great Lakes and a small 

 area in the Gulf region encroaching respectively upon the 

 northern and southern zones. The natural phytogeographical 

 areas, however, are by no means determined by latitude alone, 

 this being especially the case in the central zone, where there 

 are several quite unrelated floristic regions lying in practically 

 the same latitude. Such, for example, are the eastern forest area 

 and the western Cordilleran region. 



The pronounced continental climate of the great plains, with 

 its yearly range of temperature from arctic cold to tropic heat, 

 may be contrasted with the uniform mild climate of the Pacific 

 Coast, where longitude plays quite as important a role in deter- 

 mining the distribution of plants as does latitude. For example, 

 Victoria in latitude 48 has a mean temperature for January of 

 41.9° p., while St. Louis, almost 10° further south, is 12 degrees 

 colder. This illustrates the differences in the conditions between 

 the Pacific Coast region and the pronounced continental climate 

 of the Middle West. 



The southern area, including Mexico and Central America, is 

 for the most part tropical in its climate, except for the temperate 

 uplands of Mexico. Within the United States, Florida and the 

 southernmost tier of states adjacent to Mexico, really belong to 

 the southern area rather than to the central one. 



In the third part of his volume Dr. Harshberger treats at 

 great length the geologic history of North America, and its bear- 

 ing upon the origin and distribution of the present flora. In 



