Plant photoperiodism in the new National Academy of Sciences and National Research Council building is shown in Washington, D.C. The change in relative length of day and night with advance of the seasons and with change of latitude is an important factor in the periodic behavior of plants and in their natural distribution. In many species, flowering and fruiting and other features of development may be controlled at will by appropriate regulation of the number of hours of daily illumination. The exhibit shows plants requiring from 24 hours to 8 hours a day of light being fed artificially.

Photo is dated 1924.

Photo measures 10 x 8.25 inches.