CH. iv] Effects of Frost and of Sunshine 59 



and of the more recent calculation by Sir W. N. Shaw 

 that every inch of rain falling during the autumn 

 months September, October, and November blowers 

 , the yield of wheat during the next season in the eastern 

 counties by a little over 2 bushels per acre (2*2 to be 

 precise) from an ideal standard of 46 bushels per acre. 



The older writers, noticing the value of frost and 

 snow, thought they had an actual fertilising value, and 

 indeed many gardeners and farmers will still contend 

 that snow is a manure. Opinions of good cultivators are 

 always entitled to respectful consideration, and many 

 analyses of snow have been made, but they have failed 

 to reveal any appreciable amount of fertilising con- 

 stituents. Snow differs a little from frost in its action: 

 it forms a non-conducting coat for the soil and prevents 

 the temperature from falling as low as it otherwise 

 would. Any plants that happen to be in the soil benefit 

 by the snow cover because their roots are protected from 

 excessive cold. 



A hot dry summer has at least as beneficial an effect 

 on the soil as a cold dry winter. The drying out cer- 

 tainly changes a heavy soil into clods, but when these 

 are moistened again by autumn rains they readily fall 

 to a good tilth. If the warmth has been sufficient there 

 is an even more marked improvement in the soil popu- 

 lation as far as food-making is concerned than after a 

 cold winter. 



The effect of season on the nitrate content of the soil. 

 The manufacture of nitrates in the soil (which, as we 

 have seen, is an indispensable process for the welfare 

 of the crop) takes place most rapidly in our climate in 

 late spring or early summer. It then slackens down 

 while the plant is growing, but it may speed up again 



