56 



VEGETABLE GARDENING 



readily transmits the water upwards to the surface soil in 

 the same manner that a lamp wick carries the oil to the 

 flame. At the surface the soil water is prevented from 

 evaporating by the blanket of loose earth, and is thus 

 saved in the upper subsoil and lower and middle parts of 

 the furrow slice for the roots of the crop. Loose surface 

 soil is a good non-conductor of water. During the growth 

 of a crop the surface soil should never be left long with a 

 crust on it, but should be stirred after each rain or arti- 

 ficial watering. 



Cultivation to Develop Plant Food. Nearly all virgin 

 land contains immense quantities of plant food. Professor 



Fig. 12. Illustrating the efficiency ot the fine-tooth cultivator. 



Snyder has shown that our average wheat-producing soils 

 contain enough nitrogen to raise one hundred and twenty- 

 five successive crops of wheat. But only a very little of 

 this material is ever at one time in a condition in which 



