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admissible shortening of the vegetative period of growth. To overcome this 

 difficuhy the seed must be changed since the method of cultivation will not 

 permit the return to normal seeding. 



DiAPHYSis (Growing Out) of the Potato. 

 In summers with little rainfall, as, for example, in 1904, one of the 

 most frequent complaints was that the potatoes remained small or when ap- 

 proximately normal size, showed an uncommonly large formation of sec- 

 ondary tubers (" Kindelhildung" ) . In Fig. 17 is illustrated one of the most 

 bizarre forms, which shows two kinds of diaphysis (growing out), viz., the 

 actual "formation of secondary tubers" and "water ends." The stem end 

 of the tuber (at the left side in the drawing) shows two daughter tubers 



Fig'. 17. Proliflcated potato; at the left the beginning' of complete lateral tubers; 

 at the right, subsequent elongation of the tip end (water ends). (Orig.) 



growing on either side at about the same relative position like the arms of 

 an armchair. Toward the tip we find the daughter tubers becoming smaller 

 and smaller, until near the conical end of the tuber (right side of the 

 picture) they are recognizable only as small hemispherical processes. 



This malformation is caused by Prolepsis, i. e., a premature or hurried 

 development of the eyes. The explanation of this phenomenon is easily 

 found. After prolonged foliage development the underground eyes of the 

 potato plant develop tubers which store the already manufactured starch. 

 The drier the summer, the more quickly the tuber ripens, since, with the 

 regular enlargement and increase of its cells, the starch grains enlarge and 

 the cell walls thicken. The cells (except the youngest about the eyes) grad- 

 ually lose the ability to increase in size to any extent. 



If now, after prolonged drought and advanced ripening, a considerable 

 amount of water is forced up into the tuber, this abundant absorption of 



