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THE AMERICAN NATURALIST [Vol. XLIII 



America show a remarkable coincidence with the natural 

 vegetation centers. If future work both on climate and 

 plant distribution should bring these fundamentally dif- 

 ferent view-points into essential agreement we should 

 have the possibility of a completely dynamic and genetic 

 system of vegetation and climatic units. 



2. Sources of Error in Applying Climatic Data. -One 

 of the sources of confusion in the use of the climatological 

 data supplied by the Weather Bureau, in connection with 

 vegetation studies, lies in the placement of the instrument 

 shelter. The data derived recently by means of recording 

 instruments placed in various topographic situations, 

 show such great comparative variations, that the applica- 

 bility of meteorological records made under the condi- 

 tions represented by some of the weather stations may 

 be called into question. Fortunately descriptions of the 

 climatological stations of the United States are now 

 available 3 and selection of stations which truly represent 

 the conditions of at least one local habitat may be made. 



A second source of error in the comparison with vegeta- 

 tion of climatic data as represented on charts is the fact 

 that the means do not always represent actual local con- 

 ditions, but may have been corrected for altitude above 

 sea level. Such corrections, however, have not been made, 

 except in the case of the barometric pressure maps, in the 

 recent climatological bulletin of the Weather Bureau. 



3. Recording Instruments for the Measurement of the 

 Climatic Factors.— The increasing number of those who 

 are attempting to secure by means of recording instru- 

 ments, habitat data regarding temperature, relative hu- 

 midity, etc., is the most hopeful sign of progress in the 

 solution of the climatic problems of plant distribution. 

 We now have fairly satisfactory recording instruments 

 for temperature, humidity, rainfall and sunshine. The 

 porous cup atmometer recently added to this list places 



'Henry, A. J. "Climatology of the United States," Bull. Q, U. S. 

 Dept. Agric, Weather Bureau, 1906. 



