A GROWTH-INHIBITING SUBSTANCE 245 



resents three seasons' growth. The slow growth of the second 

 season (during which time the shoot was erect) did not prevent 

 the development of fruit spurs from A to B on the wood of the 

 previous year. The weight of the branch in the second season 

 plus the weight of fruits bent the main axis into an approximately 

 horizontal position. 



The growth which occurred in the third season was very 

 characteristic. The growth of the previously formed spurs (be- 

 tween A and B) depended entirely upon their position. Those 



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Fig. 3. A pear branch which changed from the vertical to the horizontal posi- 

 tion after fruit spurs from A to B had been produced. See text for explanation. 



which lay close to the " dorsal line" of the branch developed 

 into vigorous shoots (about 55 cm. each); those situated on or 

 near the "lateral lines" of the branch grew less (5 to 20 cm. 

 each) ; those situated on the " ventral line" of the branch scarcely 

 grew at all in length (0.6 to 1.5 cm.). 



The portion between B and C, which possessed no lateral shoots 

 at the time the branch assumed a horizontal position, produced 

 several shoots following the very slow growth at the apex. Here 



