p. F. WAREING 



and 

 T. A. VILLIERS^ 



University College of Wales 



Growth Substance and Inhibitor Changes in 

 Buds and Seeds in Response to Chilling 



During the past 50 years, a number of hypotheses have been put for- 

 ward to account for the phenomena of dormancy in plant organs. 

 Since the discovery and isolation of plant growth hormones, however, 

 many workers have attempted to explain dormancy in terms of these 

 substances. Since the ability for growth is in some way arrested in 

 dormant tissues, it is clear that dormancy is closely linked with gen- 

 eral problems of growth control, and it is reasonable to consider 

 how far the alternating cycles of growth and dormancy shown by 

 many plants are controlled by specific growth substances. 



Now dormancy can be envisaged as being due either to the lack 

 of certain essential growth factors or to the presence of active growth 

 inhibitors. Certain earlier authors suggested that the inability of 

 dormant tissues to grow may be due to lack of auxin, and indeed sev- 

 eral workers found that auxin appears in buds only in the latter part 

 of the winter (2, 4, 24). It seems unlikely that dormancy is controlled 

 primarily by auxin deficiency, however, since application of exoge- 

 nous auxin is generally not effective in breaking dormancy. On the 

 other hand, others have concluded that dormancy of buds is caused 

 by the presence of supraoptimal concentrations of auxin (7, 17), but 

 this view is difficult to reconcile with the fact that auxin levels are 

 very low during the early stages of bud dormancy. 



The view that bud dormancy may be due to specific growth-inhibit- 

 ing substances was first put forward by Hemberg (10 to 14), who 

 showed that the peel of dormant potatoes and the bud scales of Frax- 

 imis excelsior contain growth-inhibiting substances, and that when 

 dormancy is broken by chilling or treatment with ethylene chlorhy- 



^ Subsequently: Botany Department, Makerere College, Kampala, Uganda. 



[95] 



