246 H. S. REED AND F. F. HALMA 



again, buds on or near the dorsal line produced much larger 

 shoots than those near the lateral lines. Buds situated on the 

 ventral line were mainly dormant and those which did grow pro- 

 duced shoots less than 1 cm. long. 



We may now proceed to analyze the growth phenomena of 

 the branch in the light of our previous discussion. 



The writers have previously shown that horizontally sus- 

 pended cuttings of the Chinese lemon produce new shoots only 

 from the dorsal side. The behavior seems to indicate that the 

 inhibiting substance accumulates along the ventral side of a 

 horizontal shoot. 



If we assume that a similar condition exists in the pear tree 

 branches, we shall have a logical explanation for what occurs. 

 In a branch such as shown in figure 3, growth takes place vigor- 

 ously from the dorsal side, because that region is freest from the 

 growth-inhibiting substance; growth along the ventral line of 

 the branch is almost totally inhibited because the growth-in- 

 hibiting substance is there most abundant. There is no reason 

 whatever to assume that the buds on the ventral side of such a 

 branch are in any way less capable of development than those 

 on any other side. Had the branch been bent in the opposite 

 direction, the type of growth would have been the same, though 

 produced from buds on the opposite side of the branch. 



If it were a question of the relative abundance of food sub- 

 stances, we should expect the opposite result, since it is difficult 

 to see how the upper half of the branch could be filled without 

 also filling the lower half. 



It need not be assumed, however, that the movement of this 

 hypothetical substance is wholly dependent upon the pull of 

 gravity. It will be seen that in the basal portion of a horizontal 

 branch the growth, even of dorsal shoots, is more and more re- 

 stricted until finally buds are reached which are wholly dormant. 

 It seems logical to assume that the inhibitory substances are 

 principally carried in the basipetal stream of elaborated materi- 

 als which travels in the phloem and are secondarily influenced 

 by the pull of gravity. 



