Polarized Growth and Cell Studies in the First Internode and Coleoptile of Avena in Relation to Light and Darkness

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Abstract
Internode and coleoptile lengths differed markedly in 20 vars. of 3 spp. of Avena, and differed according to light and dark treatment in early germination. In A. sativa var. Victory, grown under different intensities of light, internode length varied inversely with intensity, and inhibition of elongation took place at intensities below 0.1 erg/mm2/sec. While very low as well as high intensities of light inhibited growth in length of the first internode, only high intensities shortened the coleoptile (by decreasing the number of cells as well as cell length). Both cell division and cell enlargement were responsible for polarized growth; during early germination, cell enlargement was found to occur in the 1st internode whether seedlings were grown in light or darkness: in later development, cell division occurred in darkness and in very low intensities, but not in bright light. The effect of light in shortening the 1st internode of the axis was brought about primarily by inhibition of cell division; it is suggested that the influencing factors are probably concerned with certain substances necessary for cell division, and, if so, such substances must be rendered ineffective, or are changed in their path of movement, by very low intensities of light.

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