NUTRIENT REQUIREMENT OF THE POTATO 



331 



All the plants were very much under size and the new tubers 

 that had formed were small. The difference in growth of tops 

 is clearly seen in figure 2. The set of less developed plants 

 formed seven tubers averaging 4.7 grams each, while the set of 

 the more developed ones formed six tubers averaging 8 grams. 

 The growth of these plants seemed directly related to the devel- 

 opmental stage of the sprouts at the time they were separated 

 from their tubers. Appleman 2 has shown that the vigor and sub- 



Fig. 2. Differences in vigor and growth of potato plants when grown from 

 sprouts separated from their tubers at different stages of maturity. 



sequent development of a potato sprout is greatly influenced by 

 the size of the seed piece. Sprouts on seed pieces weighing less 

 than 1.5 ounces are usually weak and tend to develop into weak 

 plants. The smaller the seed piece the greater this tendency 

 becomes. The facts found by Appleman indicate the presence 

 in the old seed piece of some growth-promoting substance that is 

 needed by the growing sprout for its normal development. 



2 Appleman, C. O., Physiological basis for the preparation of potatoes for seed. 

 Md. Agric. Exper. Sta. Bull. 212. 1918. Special growth-promoting substances 

 and correlation. Science n.s. 48: 319-320. 1918, 



