CH. I.] SOWING. 47 



These facts hold out some beacons worthy of being 

 attended to, as guides for the operation of sowing. 

 They point out that eveiy kind of seed has a par- 

 ticular depth below the sui'face, at which it germi- 

 nates most \dgorously, as securing to it the most 

 appropriate degree of moisture, of oxygen gas, and of 

 warmth. From a quarter of an inch to two inches 

 beneath the siuface, appear to be the limits for the 

 seeds of plan.s usually the objects of cultivation; 

 these, howev r, must x-ary for the same seeds in 

 different grounds and countries. It must be the least 

 in aluminous soils and dry climates. In general, sow- 

 ing should be performed in dry weather, especially on 

 heavy soils, not only because of the greater saving of 

 labour, but because it prevents the seed being 

 enveloped with a coat of earth impermeable by the 

 air, " which,"' says Sir H. Davy, " is one cause of the 

 miproductiveness of cold, clayey soils." Perhaps the 

 time at which any ground may be raked with the 

 greatest facility, is as good a practical criterion as 

 any, to judge when it is most fit for sowing. In 

 general, if clay does not predommate in its constitu- 

 tion, a soil rakes best just after it has been turned 

 up with the ^] ade. If clay does predominate, it 

 usually rakes ^rith most facility after it has been dug 

 two or three days, and then immediately after a gentle 

 rain. But it is ceitain that the sooner seed is sown 

 after the soil is dug for its reception, the earlier it 



