171 



Another study into the total riuliation received by the phmts in 

 sunshine was made by Gasparin by phicing a thermometer in the cen- 

 ter of a <>h)be 1 decimeter in diameter, made of thin copi)er and cov- 

 ered with a layer of laini)black. Having found by comparison that 

 Inilbs of dili'ercnt sizes gave diti'erent temperatures, he recommends 

 this size to all meteorologists; but I do not know of observations 

 made by others until Violle (1879) urged the same construction and 

 size for his conjugate bulbs. This bulb in the full sunshine and at a 

 standard distance above the ground seemed, to Gasparin, to give 

 what he calls the temperature of a dry opaque body. The differ- 

 ence betAveen this and the temperature of the air gave a surplus show- 

 mg the effect of solar radiation on the leaves; again, the difference 

 between this dry, black, bulb and the temperature of the surface of 

 tlie moist earth gave him some idea of the nature and amount of the 

 influence of the sunshine on the surface of the soil, which he illustrates 

 by the following table, derived from seventeen years of observations : 



Teuipcrature at 2 p. vt. 



On this table (jasparin remarks: 



We see how much the difference of temperatures of the stems and 

 the roots ought to modify the flow of the sap, and there is here an 

 interesting subject for physiological study which should redound to 

 the profit of agriculture. The solar heat contributes also in a remark- 

 able manner to cause the differences in the vegtation of the moun- 

 tains and the plains. On mountain tops it is the heat of the surface 

 soil and the roots in the sunshine and the effect of sunshine on the 

 leaves that makes possible the existence of a great variety of phieno- 

 gams. The direct action of the solar heat is the explanation of the 

 {possibility of raising cereals and other southern croi)s in high north- 

 ( rn latitudes. 



(lasparin (1852. p. 100) gave the following table, compiled for west- 

 ern Europe, showing the mean temperatures of the day during which 

 the respective plants leaf out, flower, or ripen. This early effort to 

 ni)ply meteorological data to the study of plants takes no account, as 

 the author himself says, of other meteorological conditions than tem- 

 perature such as introduce considerable variations into the pha-nolog- 

 ical phenomena, but he gives it in hopes of helping thus to fix the rela- 



