208 



EXPERIMENT STATION RECORD. 



Figure 7 gives a graphic representation of the temperature at different 

 depths. Temperature affects plants differently according to the depth 

 of their roots. At 0.05 meter, for instance, is given the temperature for 

 the germination of seed. The maximum, and especially the minimum, 

 temperatures are most important. The highest average temperatures 

 in winter were those at a depth of 1 meter, while in summer the highest 

 temperatures were at the surface of the soil and the lowest at a depth 

 of 1 meter. There is an inversion in the spring and in the autumn. 



JAN. FEB. MAR. APR. MAY. JUNE JULY AUG. SEP 



OCT. NOV. DEC. 

 25' 



Fig. 7.— Temperature of subterranean water and of the soil at dinereut depths. 



On this account the average annual temperature is about the same for 

 all the depths. These phenomena vary somewhat from one year to 

 another, the inversions being produced more or less slowly according to 

 the heating or cooling of the soil. At times this inversion is remark- 

 able, as was the case in the spring of 189G. Sometimes it is very incom- 

 plete, as in the winter of 189G. The minimum was observed in February 

 and the highest temperature was attained in July. Hot days com- 

 pletely dry out the superficial layers of the soil, and high temperatures 

 are, unless accompanied by a sufficient rainfall, injurious to plants. 



