PRINCIPLES OF PLANTING AND CULTIVATION 37 



roller or wheel is flat or concave, so that the soil over which it 

 passes is compacted over the seed. Sometimes the press wheels are 

 made very narrow, while in other cases they are as much as 3 inches 

 wide. The width is determined by the diameter of the wheel, the 

 load carried by the drill, and the crop planted. Grain drills used 

 in agricultural practices are provided with narrow wheels placed 

 immediately behind each drill tooth. These have considerable 

 weight and compact only a very narrow strip of the soil over the 

 seeds. Such drills are called press drills. The seed drills used by 

 market gardeners are provided with a following wheel, usually hav- 

 ing a concave surface. This wheel is about 6 or 7 inches in dia- 

 meter with a surface 2j to 3 inches wide and has considerable 

 weight. These operations are of much more importance than is 

 generally supposed, and it is worth one's while to carry on some 

 demonstration tests to prove the value of the different methods 

 of covering and treating the seed at planting time. 



Thinning. Crops which are grown in the open from seed sown 

 in place are usually planted much too thick, in order to secure a 

 proper stand of plants. It is necessary, therefore, to thin them in 

 order to give room for full development. This thinning is done 

 not only to give the plants an opportunity to expand their leaves 

 properly but also to provide them with a sufficient area from which 

 to gather food. Thinning should therefore be done as soon as 

 possible after the plants are up, in order that those which are to 

 remain shall not, in any way, be hampered in their growth by the 

 competition of plants which are later to be eliminated. This early 

 elimination prevents the wasting of the available food of the soil, 

 because the food which has been taken up and used by the plants 

 which are afterwards destroyed is lost so far as that season's growth 

 is concerned. 



Thinning is accomplished in various ways according to the crop. 

 There are several implements designed as weeders which serve the 

 purpose of thinning or chopping out. The thinning of cotton is 

 generally done with a broad hoe and is called " chopping out." 

 With beets, which are to stand much closer than cotton plants, 

 chopping out is also practiced, but it is generally done with a narrow 

 hoe. Sugar beets, garden beets, and onions are usually thinned 

 by hand or with a small hand implement similar to that shown in 



