8 H. O. HALVORSON 



able temperature, light, humidity; a nutrient supply; and 

 certain conditions of equilibrium within the plant^-^. If a bud 

 remains dormant for more than a year after its formation, it 

 usually becomes latent, in which case it will open and grow 

 only under rather unusual conditions'-^. 



Under normal conditions, buds will remain dormant only 

 during the winter months. The exposure to the low temperatures 

 of winter appears to be an essential feature in the breaking of 

 the dormancy. When the warmer temperatures occur in the 

 spring, the buds will begin to grow normally. The need for this 

 exposure to the low temperatures of winter has been evidenced 

 in some of the warmer climates where in certain years the 

 temperature does not get low enough to properly condition 

 these buds. Such buds, when they do begin to grow in the spring, 

 are abnormal; and any flowers that are produced, are irregular. 

 The cause of dormancy in buds is not well understood. Some 

 believe it is due to a lowering of the oxygen level, but apparently 

 this cannot be substantiated by the experimental evidence that 

 is available. Considerable research has been directed toward 

 breaking this dormancy by chemical means. For this purpose, 

 ethylene, chlorohydrin, thiocyanates. thiourea, dinitrocresol, 

 and dinitrophenol have been used, but there are many buds 

 which do not respond to these chemicals. 



Latent buds may remain in the bark of the tree during the 

 entire life of the plant and, as mentioned earlier, grow only 

 under very unusual conditions. These latent buds are not loose 

 in the bark, but continue to be attached and directly connected 

 with the annual ring from which they originate. When a limb or 

 stem of some size is cut, the numerous shoots that spring from 

 near the cut edges of the bark come from these latent buds. 

 These are som.etimes called adventitious buds. Practically 

 nothing is known about the trigger mechanisms that initiate 

 growth in these, but certainly this is nature's way of providing 

 a mechanism for growth of the plant if the normal buds are 

 destroyed. The most interesting examples of this that I have 

 seen, are shoots that develop from these adventitious buds on 



