DORMANCY IN BUDS 253 



No one metabolic change induced by effective bud-forcing chemicals 

 throws much light on the mechanics by which these chemicals initiate the 

 gro\vth of dormant buds. The situation is little, if any, better if one con- 

 siders all the metabolic changes. Perhaps this is to be expected since the 

 changes studied were largely in the storage organs rather than in the grow- 

 ing parts of the buds themselves. Another difficulty is the fact that so 

 many metabolic changes induced by these chemicals have been found 

 already, and there are probably many others still to be discovered. The 

 great number of changes make it impossible to select any one that holds a 

 causal relation to bud forcing; indeed it is a question whether any one 

 hiduced metabolic change holds such a relation. This failure of the study 

 to connect some one metabolic change with initiation of bud growth does 

 not subtract from the value of the study. The facts learned and principles 

 established add much valuable knowledge on plant metabolism and on the 

 effect of chemicals upon plant metabolism. The whole study, and espe- 

 cially the work on the synthesis of glycosides, shows to what a degree the 

 chemical composition of plant organs can be modified by the introduction 

 of a foreign chemical into plant organs. 



Summary 



A rest period is common for buds of tubers, bulbs, and trees of the tem- 

 perate zone. Buds of potato tubers remain dormant for a period of 9 to 

 12 weeks in ordinary storage. The period is shortened by storage at a high 

 temperature, 35° C (95° F), and by moist storage that favors development 

 of cork periderm. Buds of corms and cormels of gladiolus, of many bulbs, 

 and of trees and shrubs are thrown out of dormancy by periods of low- 

 temperature storage, 1° to 15° C (34° to 59° F). Cormels of some varieties 

 of gladiolus do not completely after-ripen even after six or seven months 

 of cold storage. A low-temperature period is necessary for the initiation 

 of flower buds in many plants or plant organs. 



In the researches reported in this chapter several chemicals were dis- 

 covered that throw buds out of dormancy. Ethylene chlorhydrin proves 

 especially desirable in practice; as it is soluble in water and has a high vapor 

 pressure, it can be used either for dip treatment or for vapor treatment. 

 It has a rather wide margin of dosage between forcing and toxic action. 

 Sodium, potassium, and ammonium thiocyanates in water solution are 

 also effective as bud forcers for potato tubers. These must be used for 

 soak treatment because of lack of vapor pressure. 



Thiourea in water solution proved fairly effective as a bud forcer. It 

 shows peculiar effects in that it breaks up the growth correlations between 

 the several buds in an eye or the several eyes in a seed piece or whole tuber. 

 As a result, thiourea treatment of potato tubers causes several buds to 

 grow in each of several eyes instead of one bud from an apical eye, as occurs 

 in storage-after-ripened tubers, or tubers treated with other bud-forcing 

 chemicals. 



