MOTIVE POWER 



485 



cleared land full of small roots, and hard dry soils where 

 it was impossible to use horse-drawn plows (Fig. 375). 



After Holt Manutacturmg Co 



Fig. 374. A '"caterpillar" gas tractor 



The number of plows drawn is dependent upon the size 

 of the tractor, A tractor of sufficient power to perform the 

 heaviest work required of it is purchased, and the number 

 of plows is then adjusted to its strength. On the ordinary 



After J. I. Case Threshing Machine Co. 



Fjg. 375. A gas tractor drawing three plows 



farm a tractor capable of pulling two or three plows, with 

 the preference for the three-plow size (Fig. 375), has been 

 found to be the size best suited to other work. The average 

 number of acres plowed per day per plow decreases as the 



