CHAPTER 7 



Dormancy in Buds 



A rest period is general for buds of tubers, bulbs, and woody plants. 

 This is especially true of temperate-zone plants. The duration of dormancy 

 in buds of potato tubers varies from 9 to 12 weeks, depending on the variety, 

 when stored at an- temperatures. It is not shortened by storage at low tem- 

 peratures but is shortened ^^ considerably by storage at 35° C (95° F), as 

 well as by storage with high moisture.^' Low-temperature storage is very 

 significant in shortening the rest periods of buds of many bulbs, such as 

 the gladiolus. It is also important in inducing flowering in bulbs and in 

 certain biennial ^ and perennial plants. After havmg plants of Crassula 

 rubicunda about the greenhouse for years without flower production, 

 Arthur induced profuse flowering by exposing the plants to low tempera- 

 ture for a few months. Flower induction by low-temperature exposures 

 has been termed ^ thermoperiodism. When seeds are made to produce 

 plants that flower earlier by exposing them to low temperatures the process 

 is referred to as yarovization or vernalization. The physiological changes 

 involved in thermoperiodism and yarovization are probably similar. Buds 

 of temperate-zone trees and shrubs go into dormancy in late summer and 

 are thrown out of this condition by the cool weather of faU, winter, and 

 sprmg. As in low-temperature after-ripening of seeds, temperatures be- 

 tween 0° and 10° C (32° and 50° F) are effective ^ for buds of various kinds 

 of trees and shrubs, but higher temperatures and temperatures below 

 freezing are not. 



Dormancy in Potato Buds 



Attempts have been made to force dormant buds by the use of anesthe- 

 tics 68. 69, 70 without great success. As we have already seen, ethylene and 

 certain plant hormones which are good anesthetics inhibit bud growth, at 

 least as long as they are in contact with the buds. McCallum ^^ found 

 ethyl bromide especially effective in overcoming dormancy of potato buds. 

 He exposed the tubers to 1 to 2 cc of the chemical for 24 hours in a 5-liter 

 air-tight jar. Appleman ^ found that buds of potato tubers grew more 

 rapidly if the tubers were kept moist. He concluded that moisture pre- 

 vented the development of the corky periderm which reduced the oxygen 

 supply to the buds. Thornton,^^ {^ ^ paper that was awarded the A. Cressy 

 Morrison Prize as an outstanding paper in biology in 1938 by the New 

 York Academy of Sciences, confirmed Appleman 's result that potato 



230 



