114 FARM MACHINERY 



and trashy ground. The single disk has one objection, 

 and that is that it tends to make the ground uneven, since 

 the soil is thrown in only one direction. 



The double-disk furrow opener has two disks, or really 

 coulters, as they are flat and their action is much like that 

 of the shoe. One disk usually precedes the other by a 

 short distance. The double-disk has not the penetration 

 of the single-disk, but will not ridge the ground as the 

 single-disk does. They often have another bad feature 

 in that they allow dry dirt to fall on the seed, and hence 

 prevent early germination. The single-disk drill does 

 more to improve the tilth of the ground than any other 

 furrow opener. The fact that a slight ridge is left in the 

 center of the furrow with the double-disk is considered 

 by some an advantage, as the seed is better distributed; 

 in fact, two rows are planted instead of one. 



149. Interchangeable parts. Most manufacturers now 

 design their drills in such a way that any one of the 

 various styles of furrow openers may be used. Fig. 85 

 shows furrow openers which may be used on the same 

 drill. 



150. Press wheels. Not a few years ago drills were 

 equipped to a large extent with press wheels, but now 

 they are not so popular. The press wheel, when sufficient 

 pressure can be applied, is evidently a very good thing, 

 as the earth is compacted around the seed and the 

 moisture is drawn up to the seed, causing early germina- 

 tion. The pressure upon each press wheel must neces- 

 sarily be very small, as most of the weight of the drill is 

 required to force the furrow openers into the ground, and 

 the balance is to be divided over a number of press 

 wheels. It is not an uncommon thing to see an old drill 

 running with some of the press wheels entirely off of the 

 ground. Drills have been made in two distinct types, one 



