Defoliation and decapitation experiments showed that the growth of a grapevine leaf was inhibited by both the terminal bud and the younger higher leaves. There is a phenomenon of synergy between these two influences. A young leaf freed of these two influences showed a higher growth rate than the norm ; this is « compensatory growth ». It is when a leaf is in its phase of maximal growth that it is most able to realize this « compensatory growth ». This is not due to a longer growth time, but more to a faster growth rate. This « compensatory growth » is not the consequence of competition between leaf growth and internodal elongation. Exogenous applications of auxins prevented or restricted this growth; gibberellic acid had no effect. These results partly explain those of other authors who demonstrate that reduction in the leaf area of a vine is accompanied by an increase in photosynthetic efficiency of the remaining leaves.
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