gg BOTANICAL GAZETTE [February 



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logical stations is entirely inapplicable to the subject under considera- 



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tion. 



For ecological purposes temperature observations in the field have 



to be made very carefully if we are to draw from them any conclusions 



of value as to the influence of heat on the vegetation. And further, they 



have to be extended over a long period of years before we are justified 



in advancing any general laws of temperature influence on distribution 



of plants. 



Let us here draw attention to the opinion held on this question by 



the greatest authority on ecology, Professor Warming. In his re- 

 nowned handbook on ecological phytogeography (14) he says on page 

 22, speaking of the many attempts to determine the sum-totals of 

 temperature in relation to geographical distribution, that these investi- 

 gations need in a very high degree to be supported by really scientific 

 experimental determinations of the cardinal temperatures for the 

 phenomena of different species. And even the results of such observa- 

 tions would hardly be sufficient for the solution of the very difficult 

 and complicated questions of the importance of heat conditions for 

 distribution of species and phenological phenomena, as other factors 

 perhaps, to some extent can replace a higher temperature. 



One feature of the heat conditions on coastal sands is apparent. 

 That is the great fluctuation of diurnal temperatures. On account 

 of the low specific heat of sandy soil, the surface layers are rapid!) 

 heated by the sun in daytime and as quickly cooled by night. These 

 variations of temperature are conducted by radiation to the lower 

 strata of the atmosphere, or those in direct touch with the plant 

 which consequently are greatly affected by such changes. 



Of seme occasional observations by the writer on the diurnal range 

 of temperature on sand dunes the following may be mentioned as 

 examples of the great divergence between temperature extremes m 

 such localities. 



Observation 64.— Dunes at Hango, Finland, September 10, 1897. Maximum 

 temperature in the shade (thermometer from unknown maker) 28^8 C, between 

 6 A. m. and 6 p. m Minimum (thermometer from Wallmann in Stockholm 

 2?6 between 6 p. m. and 6 A. m. Range 25*6. The instruments were pla ced 

 on an open sand surface 25 cm above the ground, and were shaded by white 

 canvas, 2" 1 high. Ordinary thermometer readings in the shade were taken 

 every hour in the daytime, giving the following results: 



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