Dr Forry on the Climate of the United States. 213 



iron in it is held to be peroxide ; and pyrope, although it 

 yields in that way, a black glass also, aflForded to Klaproth 

 a grey or brown glass in a crucible. 



Researches in Elucidation of the Distribution of Heat over the 

 Globe, and especially of the Climatic Features peculiar to the 

 Region of the United States. By Samuel Forry, M.D., 

 Author of " The Climate of the United States, and its 

 Endemic Influences," Editor of " The New York Journal 

 of Medicine and the Collateral Sciences," &c. 



(Concluded from page 105.) 



Another important subject is the influence of temperature 

 on the geography of plants, which has been ably treated by 

 M. De Candolle. In considering its relation with the organic 

 life of plants, it is necessary to keep in view three objects : — 

 1. The mean temperature of the year. 2. The extreme mean 

 temperature both in regard to heat and cold. 3. The distri- 

 bution of temperature among the difi"erent months of the year. 

 The last is the most important ; but in the investigation of ve- 

 getable geography it is requisite to estimate the simultaneous 

 influence of all physical causes, — soil, heat, light, and the state 

 of the atmosphere, as regards its humidity, serenity, and vari- 

 able pressure. Each plant has generally a particular climate 

 in which it thrives best ; and beyond certain limits it ceases 

 to exist. Hence, having seen the great variations of summer 

 and winter temperature on the same isothermal line, the ab- 

 surdity of limiting a vegetable production to a certain latitude 

 or mean annual temperature, is apparent. To say that the 

 vine, the olive, and the coff'ee tree require, in order to be pro- 

 ductive, annual temperatures of 53° 60', 60° 80', and 64° 40', 

 is true only of the same system of climate. As the annual 

 quantity of heat which any point of the globe receives varies 

 little during a long series of years, the variable product of 

 our harvests depends less on changes in the mean annual tem- 

 perature than in its distribution throughout the year. Thus, 

 climates, in regard to vegetable productions, are strongly 



