Effects of Controlled Shading upon the Development of Leaf Structure in Two Deciduous Tree Species

Abstract

Numerous descriptions and illustrations of differences in structure of leaves of plants of the same species from exposed and shaded habitats are to be found in the literature. Leaves from exposed places are designated as leaves and those from shaded places as leaves. No definite procedure has been followed by most investigators in selecting sun and shade leaves for examination. Those of herbaceous plants were often from very different and widely separated habitats. The samples of tree species were from various parts of an individual tree or from different trees, even from trees growing in widely separated regions. In each case there have been several environmental variables which might have induced the observed effects. Granting that the authors have drawn the best possible inferences, they have not been able to separate the effect of light intensity from that of the other variables. The object of the present research was to determine the effect of differences in light intensity upon cell elongation and cell division in the leaves of Cornus florida rubra Andre and Acer platanoides L. and to ascertain the stages in leaf development in which these two cell processes are most affected. It is proposed to attempt to determine by later experiments the effects of various amounts of available moisture upon these two processes within the leaf, under different light intensities. The writer wishes to express grateful appreciation to Dr. Edgar N. Transeau for suggesting the problem and for his many suggestions during its progress; to Dr. Homer C. Sampson for his valuaable criticisms and observations; and to Miss Jane Roller for her assistance with the illustrations.