THE SHOOT‐GROWTH RHYTHM OF A TROPICAL TREE, THEOBROMA CACAO

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Abstract
The shoot‐growth rhythm of tropical trees is a little understood phenomenon. Correlations of tree growth with environment, determined from field studies in the tropics, have been largely inconclusive, and few studies have been done under controlled environmental conditions. As an initial part of a project to study shoot‐growth rhythms in tropical trees this paper describes the rhythm in Theobroma cacao L. An individual shoot passes through alternate periods of growth and dormancy. The growth period is characterized by the expansion of leaves and elongation of the shoot. During dormancy the length of the shoot remains constant, and no new leaves expand. Shoot‐growth rhythm was divided into phases. Dissection of shoot tips from the various phases shows that the total number of leaves and leaf primordia in the shoot apex remains constant during the dormant period and does not increase until the onset of the growth period. This indicates that activity of the apical meristem as well as leaf expansion and shoot elongation are rhythmic. We found that the rhythm of shoot growth persists under controlled environmental conditions and that growth under these conditions is asynchronous, as it appears to be in the field. Our data strongly suggest endogeneity.
Funding Information
  • National Science Foundation (GB‐4042, 2512)