360 FIELD CROP PRODUCTION 



in a spiral form. Now if we can imagine this tuber elon- 

 gated or drawn out, these eyes would simply represent buds 

 on an underground stem, each of which could send up a 

 shoot or plant. Practically all of the higher plants have a 

 means of storing up food in some place in their tissues, which 

 can be used at a time when they need a surplus to start 

 them into growth from a dormant condition. Sometimes 

 it is in the form of starch, or it may be sugar or oil. In 

 the apple tree this food is found about each bud, in the 

 currant considerable food is stored in the roots ; but 

 in the potato a large amount of starch is stored in an 

 underground stem which becomes greatly enlarged — the 

 tuber. The amount of starch varies from 12 per cent to 

 20 per cent in most commercial varieties. 



CULTURAL METHODS 



380. Soil. — The prime essential of a potato soil is to 

 have it well drained. The loose and mellow condition of 

 the soil is of greater importance with this crop than a 

 large amount of native fertility. While the potato can 

 be grown on a variety of soils with success, the medium 

 light soils are usually best. A gravelly or sandy loam well 

 filled with humus is ideal because it affords good drainage 

 and yet supplies a liberal amount of moisture which is 

 necessary for a large crop. A light, sandy soil is usually 

 preferred for early potatoes. If a soil is not naturally 

 well drained, then tiling should be put in before maximum 

 results can be expected. When water stands for a part 

 of the growing season in pockets in the soil, many of the 

 plants will die out. This can be seen in the irrigated 

 sections in the west. 



381. Rotation. — Because of the serious diseases and 

 insects which attack the potato, it is well to practice a 



