PLANT ANATOMY AS CONDITIONED BY LIGHT INTENSITY AND SOIL MOISTURE

Abstract

The effect of physical factors on the structure of leaves has long been a popular subject for investigation. Most of the researches have been concerned with plants growing under field conditions, only a few having dealt with the effect of a given factor under controlled conditions. Furthermore, few of the studies on ecological plant anatomy have been concerned with the structure of roots and stems and few experimental data are available on those plant parts. An attempt has been made in the present investigation to determine the effects of varied light intensity and soil moisture on the structure of roots, stems, and leaves of selected species of plants. Isolation of a factor such as light intensity is difficult under field conditions since low air temperature and high relative humidity are usually associated with a low light intensity. However, it has been found possible to obtain a variation in light intensity without appreciably affecting either the air temperature or humidity by means of a specially constructed shade shelter. The leaf temperature is nevertheless affected, a difficulty thus far impossible to overcome. Modification of water content is more easily attained without greatly affecting other physical factors. It is to be noted, however, that the maintenance of an even distribution of water in a comparatively dry soil is very difficult. This is especially true since roots may absorb water in their immediate vicinity faster than the soil can supply water to them. An experiment in the summer of I926 dealing with the effect of light intensity was conducted in a clearing at the southeast corner of the University Woods near Urbana, Illinois. A later one was conducted in a garden in Urbana in the summer of I927. The preliminary soil moisture studies were made in the University of Illinois greenhousesin I926 and a more detailed investigation was carried on in a garden at Urbana in the summer of 1927.