. Auxins and plant growth. Auxin; Plant growth promoting substances. 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 i
. Auxins and plant growth. Auxin; Plant growth promoting substances. 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. 0 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).. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Leopold, A. Carl (Aldo Carl), 1919-. Berkeley, University of California Press
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