242 H. S. REED AND F. F. HALMA 



The writers 3 have also shown that there is support for the idea 

 that a growth-inhibiting substance exists in the shoots of the 

 Chinese lemon which determines to a large extent the sequence 

 of events in a regenerating shoot. It was shown that upright 

 shoots remain unbranched, except for a few laterals near the 

 apex. If the original shoot be fixed in a horizontal position, 

 buds on the dorsal side will promptly develop; hence there must 

 be something which perpetuates a condition of dormancy in the 

 buds on the vertical shoot. 



Some salient relations between the growth-inhibiting substance 

 and the course of development were shown by the growth of new 

 shoots on cuttings of the Chinese lemon. The results of these 

 experiments gave strong support for the assumption that there 

 is a substance produced in the apical region of the growing lemon 

 shoot and that it travels through the phloem toward the basal 

 region of the shoot. This substance seems to be the cause of 

 dormancy in the subapical buds. According to this theory the 

 apical buds on a cutting are the first to develop because they are 

 the first to be freed from the inhibitory substance. As soon as 

 the apical buds develop new shoots, they also produce the in- 

 hibiting material which migrates toward the basal buds and per- 

 petuates the condition of dormancy. 



It does not appear that the movement of the growth-inhibit- 

 ing substance in a cutting is directed solely by the pull of gravity, 

 because the progress of growth in an inverted vertical cutting is 

 practically the same as in a cutting in normal vertical position. 



Any bud on a cutting will develop if one removes a piece of 

 bark and phloem immediately above the bud because the in- 

 hibiting material from the apical regions is thus prevented from 

 reaching the bud. 



The growth of sprouts on a potato tuber affords confirmatory 

 evidence of the presence in them of a growth-inhibiting sub- 

 stance. Appleman 4 has shown that the buds on the apical end 



3 Reed, H. S., and Halma, F. F. On the existence of a growth-inhibiting 

 substance in the Chinese lemon. Univ. of California, Publ. Agr. Sci., 4: 99-112, 

 1919. 



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

 seed. Bull. 212, Maryland Agr. Exp. Sta., 1918. 



