A STUDY OF FACTORS INFLUENCING THE YIELD OF POTATOES 1207 



Seed of these same varieties, introduced during the last four unfavorable 

 years from Nappan, Nova Scotia, and subjected to the same unfavorable 

 conditions, maintained its yield much better, showing that the vigor of 

 northern-grown seed enabled it to withstand adversity better than home- 

 grown seed similarly treated. Stone (1905) reported an experiment by 

 Fraser in which tubers that had been stored in a cool cellar until May 1 

 were taken out and stored for thirty-six days under four different con- 

 ditions. Yields from seed stored in a dark cellar at from 50 to 60 F., 

 in a coldframe at 80, at a barn window at out-of-door temperatures, and 

 in a greenhouse at from 70 to 90, showed about equally good results 

 from the coldframe and the barn-window storage. The seed stored in the 

 dark cellar gave decidedly inferior average yields, showing that moderate 

 light and temperature for from four to six weeks before planting improves 

 production over the usual method of dark-cellar storage up to 'planting 

 time. 



The potato crop of Maine, Vermont, and northern New York is almost 

 invariably harvested before the maturity of the plants. The vines are 

 usually killed by frost. Therefore the use of northern-grown seed for 

 Long Island means the use of immature seed; and, since immature seed 

 is closely associated with the dormancy, or rest period, of the potato 

 tubers, this question also is concerned. According to Appleman (1918), 

 the rest period varies with the variety but is fairly constant within each 

 variety. Appleman (1912) has shown that three processes go on in 

 potato tubers during the rest period: (1) respiration, or the consumption 

 of sugar by reversion to carbon dioxide and water; (2) conversion of starch 

 to sugar by diastase; and (3) change of the sugar back to starch. Since 

 these after-ripening processes are greatly influenced by temperature, it 

 follows that storage conditions have much to do with the condition of the 

 seed tubers when they are removed from storage for planting. The value 

 of seed harvested in an immature condition, which has been shown by 

 the experiments of Macoun (1905), Shepperd and Churchill (1911), Stuart 

 (1913 b), Zavitz (1916), Ballou (1910), and Gourley (1910), is due prin- 

 cipally to the fact that, the seed being immature, the after-ripening 

 processes leave it in a less devitalized condition than that of seed that 

 has entered storage fully matured. The symptom of curled skin so 

 common at harvest time on northern-grown potatoes indicates a lesser 

 degree of suberization of the epidermis than occurs in mature tubers. 

 Appleman (1914 and 1918) has shown how the rest period may be shortened 

 or broken, at almost any time, by the use of anaesthetics or of oxidizing 

 agents to facilitate increased oxygen absorption. He further showed 

 (1918) how the rest period of the southern second-crop seed may be short- 

 ened by harvesting the seed immature, spreading it on the ground, and 

 covering it with excelsior or burlap to prevent suberization. 



