194 



or the reviewer, showing the number of days between the last 

 kilHng frost of spring and the first one of autumn, would have 

 been, in the case of Dr. Harshberger's vastly greater range, of 

 the utmost possible usefulness in the orientation of our ideas on 

 plant "life-zones" of the North American continent north of 

 the frost line. In connection with the discussion of rainfall, it 

 would have added interest to make some mention of the relative 

 evaporating power of the air over different soils, as this has a 

 very marked bearing on the ultimate amount of water available 

 to the vegetation. 



The West Indies and Central America present some difficulties 

 when generalizations are attempted as to their climate. The one 

 important factor, so far as a plant geographer is concerned, is the 

 prevailing northeast trade-wind, as this has a greater effect on 

 the plant distribution than almost any other single agency. 

 Under this section. Dr. Harshberger makes only incidental men- 

 tion of this wind, but later (pp. 672-704) he ascribes to it a more 

 important position. The times and seasons of the rains in the 

 larger West Indies are controlled by this moisture-laden wind, 

 rolling in from the Atlantic and precipitating its water on wind- 

 ward slopes, leaving the drier southwesterly areas, on most of 

 the islands, all but deserts. Of all this, nothing, in the account 

 of West Indian climatology. Furthermore, in the Journal of 

 the New York Botanical Garden for January, 1910, some little 

 account of the temperature and rainfall of Santo Domingo was 

 published, based on carefully kept records for two or more years, 

 but no mention is made of this. Another feature of West Indian 

 climatology that may excite some question, as presented by the 

 writer, is the statement that the typical hurricanes originate in 

 the open Atlantic. Many meteorologists have considered that 

 these destructive storms originate in the Caribbean, just west 

 of the coast of South America, in a gigantic heat vortex, cy- 

 clonically filled up by a sudden in-rushing of cooler air. 



The third and shortest chapter (4 pages) of this part contains 

 synopses of the most important tabulations as to the number of 

 native and introduced species in North America, brought down 

 as mentioned above, only to 1908. 



