150 The Principles of Fruit-growing. 
pulverizing and fining the soil for the seed-bed, is 
most efficient in furnishing an earth-mulch. The 
spring-tooth harrow is in reality a cultivator, and 
its action is similar to that of the cultivator. 
When used as an instrument to conserve moisture, 
the teeth should penetrate to the depth of about 
three inches, and to produce the best’ effect the 
ridges left by it should be leveled off by a smoother, 
which can now be purchased as an attachment to 
the harrow. The tillage of orchards by the harrow 
is now practiced extensively, and nothing short of 
irrigation will so nearly meet the demands of trees 
for moisture, particularly upon the heavier soils. , 
The Acme harrow is a most excellent implement 
on soils which are comparatively free from stones 
and rubbish. The plow-like action of its blades 
serves to pulverize the soil, to spread the mulch 
evenly, and it leaves a most excellent seed-bed. 
The cutaway or disc harrows may be either bene- 
ficial or of absolute injury. If the discs are so set 
that they cover but a portion of the surface with 
the mulch, they leave a ridge exposed to the action 
of the wind and sun, and the rate of evaporation 
is greatly increased. The dises should be set at 
such an angle that the whole surface shall be 
stirred or covered. Their chief value lies in their 
cutting and pulverizing action on clay soils, but as 
conservers of moisture they are inferior to the Acme 
or the spring-tooth. Soils which need the disc 
harrow to pulverize them should generally be gone 
over again with some shallower tool. 
