268 Auxins in Agriculture 



thiopropanol) break dormancy. Looking back at the early searches for 

 substances wliich can break dormancy of seeds and tubers, all the 

 effective materials are either imsaturated hydrocarbons like ethylene — 

 which causes glutathione formation (Guthrie, 1933) — or they are com- 

 poinids containing divalent sidfur, such as thiocyanates, thiourea, thio- 

 semicarbazide, thioacetamide and a host of others, or glutathione itself 

 (Guthrie, 1940; Miller, 1933; Thompson and Kozar, 1939; Tukey and 

 Carlson, 1945). 1 hese materials would be expected to protect sulfhydryl 

 enzymes by simple competitive effects. It may be, then, that the in- 

 hibitors of growth which are supposedly responsible for dormancy are 

 inhibitors of sulfhydryl enzymes essential to growth. One cannot help 

 recall at this juncture the evidence discussed in chapter VIII indi- 

 cating that the stimulation of growth by auxin may be intimately in- 

 volved with sulfhydryl enzymes or coenzymes. 



Although the bvdk of evidence now indicates that dormancy is 

 essentially a fimction not of auxins but of growth inhibitors, it is 

 clear that auxins themselves can exert an effect on the capacity of a 

 potato or a deciduous tree bud to commence growth. The work of 

 Guthrie (1939) has clearly shown that moderately strong dosages of 

 auxins can inhibit sprouting and thus prolong apparent dormancy. 

 It must be remembered however, that low concentrations of these 

 same materials may have stimulatory effects upon sprouting as the 

 primary control of dormancy is removed. This makes the use of auxins 

 for prolonging dormancy a sometimes unpredictable and not com- 

 pletely satisfactory technique. 



In recent years an alternative method of prolonging dormancy 

 has been suggested by Wittwer and Sharma (1950) in which a growth 

 inhibitor is used instead of an auxin. These workers have found that 

 maleic hydrazide can effectively prevent sprouting of onions in stor- 

 age. This technique would seem to be a sounder approach to the con- 

 trol of dormancy from a physiological point of view, since the maleic 

 hydrazide would probably accentuate the natural inhibitor system 

 thought to control dormancy instead of superimposing an auxin inhi- 

 bition system instead. 



Methods of Treatment 



Of the various auxins that have been used for prolonging dor- 

 mancy, the methyl ester of naphthaleneacetic acid has achieved the 

 widest use. In preventing sprouting in potatoes the original recom- 

 mendations of Guthrie (1939) have been most commonly followed. 

 The potatoes are mixed with paper shreds or with talc containing the 



