138 FARM MECHANICS 



gen-gathering bacteria and nitrifying bacteria which 

 are often loosely referred to as azotabacter species. 

 Few of us are on intimate terms with any of them, but 

 some of us have had formal introductions through ex- 

 periments and observation. 



THE MECHANICS OF PLOWING 



Walking Plow. The draft of a walking plow may 

 be increased or diminished by the manner of hitch. It 



Figure 133. Sulky Plow. This is a popular type of riding plow. 

 It is fitted with a rolling coulter. 



is necessary to find the direct line of draft between the 

 work performed and the propelling force. The clevis 

 in the two-horse doubletree, or the three-horse evener 

 and the adjusting clevis in the end of the plow-beam 

 with the connecting link will permit a limited adjust- 

 ment. The exact direction that this line takes will 

 prove out in operation. The walking plow should not 

 have a tendency to run either in or out, neither too 

 deep nor too shallow. For the proper adjustment as to 

 width and depth of furrow, the plow should follow the 

 line of draft in strict obedience to the pull so that it 



