Dormancy and Storage 265 



reported by Guthrie, 2 mg. of the auxin gave four-fold increases in 

 the number of sprouts over the control tubers. Perhaps one can say 

 that the effects of auxin on dormancy as on bud growth may be 

 either promotive or inhibitory; that is, they may encourage the break- 

 ing of dormancy or they may accentuate dormancy. 



Although suggestions have been made that auxins may be actually 

 responsible for dormancy in a manner similar to their action in 

 apical dominance (Michener, 1942), more recent evidence now indi- 

 cates that this is very improbable. Dormant tubers and buds generally 

 lack auxin or contain only very small amounts, surely too little to 

 inhibit bud growth. In many cases measurable amounts of diffusible 

 auxin appear in the buds only after dormancy has passed. This ha^ 

 been shown for potatoes (Guthrie, 1939), some tree species (Bennett 

 and Skoog, 1938), and in other instances cited in chapter III. Careful 

 separation of auxins from growth inhibitors has led Hemberg (1949, 

 1952, 1954) to conclude that as the potato emerges from dormancy 

 there are either no changes in auxin content or the auxin content 

 may rise somewhat. His evidence is directly opposed to the concept 

 that auxins are immediately responsible for dormancy. 



A great many inhibitors of germination and growth have been 

 found to be present in various plant parts. The very wide distribution 



2 20 200 MG 



AUXIN ESTER ON PAPER SHREDS 



Fig. 109. The effect of methyl ester of naphthaleneacetic acid on sprouting of 

 potato tubers in storage at three temperatures (Guthrie, 1939). 



