EFFECTS OF CERTAIN GROWTH REGULATING SUBSTANCES ON GROWTH CORRELATION IN LETTUCE SEEDLINGS

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Abstract
In an effort to approach simultaneously the problems of growth correlation and the effects which certain reported growth-regulatory substances exert upon young seedlings. the author utilized aseptic tissue-culture technique methods to compare 4 series of cultures: (1) intact seedlings, (2) excised roots, (3) excised shoots, and (4) a combination of excised roots and excised shoots. In these 4 series, thiamin, thiourea, nicotinic acid, naphthalene acetamide, naphthalene acetic acid, and indole acetic acid were added to the culture medium of inorganic salts and sucrose in concs. from 0.01 to 10 mg. per liter. The control group (without added substances) showed that excised root growth was slightly benefited by the presence of the shoot in the medium, that the growth of adventitious roots on the excised shoot normally far exceeded that of the roots on the intact seedling, and that a further slight stimulation of this growth of adventitious roots on the excised shoot occurred when the excised root was present in the medium. When this group was compared with those obtained for the various growth substances in the lower concs., certain striking differences were seen. The usual reciprocal relationship between the root and the shoot as found in the control group was disturbed. Various morphological irregularities were observed in the higher concs. of some of the substances.[long dash]Problems concerned with the effects of growth-regulating substances on the plant must be attacked simultaneously with those on growth correlation, or any conclusions derived therefrom will be seriously limited in their scope.