The Growth of Cognate Shoots

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Abstract
A comparison of the growth processes of cognate shoots of the lemon (Citrus limonia) on upright branches which displayed an axial gradient. The longer shoots appear to owe their superiority to the presence of a larger amount of the appropriate substrates in the apical portion of the branch, as well as by inhibiting the growth catalysing substances in subapical growth centers. The superiority of the apical shoots may ultimately rest on the activity of some catalyst which effects the transformation of reserve materials. Each group of shoots had 3 well-defined cycles of growth during the season. The growth of each was expressed by the equation log x/A-x= K(t-t1). The mean velocity constants of the various cycles were logarithmic functions of A X 100/[SIGMA]A (the % of total growth produced in a cycle) and arithmetical functions of the actual growth of a cycle. In each class of shoots there were some which grew only during the 1st cycle. Their numbers were greater in subapical than in the apical groups. Their behavior suggested that the activity of their growth catalysts was stopped by some inhibitory substance which became active toward the end of the 1st growth cycle.