58 



The difference between the morning and evening temperatures 

 shows : 



(1) That the cooling during the night and the warming (hiring 

 the day is appreciably larger for the naked earth than for the various 

 kinds of litter. 



(2) That the pine needles warm up most during the day and the 

 moss Avarms up least; that the fir needles cool most during the night 

 and the pine needles least. 



The power of retaining moisture varies with the different kinds of 

 litter as follows : 



(1) Any litter of forest leaves or needles is moister than the earth, 

 but the moss is less moist than the earth ; the gradation is from oak 

 leaves, the highest, through fir needles to moss, the lowest. 



With regard to evaporation Wollny shows that the naked earth 

 loses a greater quantity of moisture by evaporation than do the 

 various kinds of litter. 



/' (2) That the moss litter evaporates the most, but the litter of forest 

 \ leaves the least. 



(3) That the quantity of evaporation is greater the thinner the 

 layer of the litter. 



In general, then, the litters of leaves and of pine needles give up 

 the rain water that falls upon them to the ground beneath in larger 

 proportion, but still continue to be very moist because they lose, rela- 

 tively, little water by evaporation; furthermore, that the moss litter 

 is distinguished by large variations in its contained water because 

 it has on the one hand a large capacity for water and on the other 

 hand a very considerable evaporating power. 



SOIL TEMPERATURES OBSERVED AT GREENWICH, ENGLAND. 



Among the limited number of long-continued series of observations 

 of temperatures of soil near the surface is that maintained at Green- 

 wich Observatory, England, since June, 1846. This series embraces 

 observations at considerable depths that will not interest the student 

 of agriculture, but we reproduce in the following table the results of 

 observations at 1 inch in depth, as given in the annual volumes of the 

 Greenwich Observatory for 1878, and as given in J. D. Everett's 

 memoir of 1860. These soil temperatures can be used in any sub- 

 sequent study of English crops throughout the southern half of 

 England or in analogous climates. 



