Potato Breeding 75 



Certain plant characters are often associated together. 

 In breeding practice a knowledge of these associations 

 is often valuable. If easily observable physical char- 

 acters, such as color of flower or texture of skin, are asso- 

 ciated with chemical composition, which is less easily 

 detected, the appearance of the former is a valuable 

 index to the existence of the latter. It has been often 

 observed that there is a certain shade of green in the 

 leaves which is correlated with vigor and high produc- 

 tivity. If the leaves are too light green, few tubers will 

 be produced, or if too dark, the yield is again small or a 

 large number of small tubers will be found, due to late 

 maturity or possibly to disease. Correlations are es- 

 pecially valuable when they enable one to select out good 

 plants in a young stage, or when they save the trouble of 

 making elaborate chemical analysis. Only a few defi- 

 nite correlations have been discovered in the potato. 

 East reports nearly all of these in Illinois Bulletin 127. 



There appears to be a positive correlation between 

 yield and the following : flat shape of tuber, number of 

 stalks to the plant and length of the growing season. 

 With a heavy setting of seed berries, we may usually 

 expect a light production of tubers. No correlation has 

 yet been found between color of the tuber and yield. 



Fischer of Germany (reported by East) says that round- 

 flat tubers tend to produce plants which are rather com- 

 pact in habit. Cylindrical tubers produce large, scraggly 

 plants. 



Round-flat tubers are richest in starch. Quality is 

 said to improve directly with an increase in starch con- 

 tent up to a certain point. An excessive amount of 

 starch causes the tuber to be coarse and woody. A 

 netted skin is usually associated with high quality. 



