Action Spectrum for Inhibition of Stem Growth in Dark-Grown Seedlings of Albino and Nonalbino Barley (Hordeum vulgare)

Growth in length of the second internode of dark-grown barley seedlings can be inhibited by a relatively small amount of radiant energy given at one or more times. 2. Both potentially green and albino seedlings of barley were sensitive to radiation, and in the variety Colsess I, which was studied in detail, they were approximately equal in sensitivity. 3. The action spectra for control of growth of the second internode of dark-grown potentially green and albino Colsess I barley seedlings were quantitatively determined but with somewhat less precision for the albino than for the potentially green seedlings. 4. The two action spectra were the same within the limits of error as those previously found for control of leaf length in dark-grown pea seedlings and for control of floral induction in both long- and short-day plants. This indicated that the phenomena depended upon the same initial photoreaction. 5. More than a thousand-fold change in energy is required to pass from a small to a large inhibition of the second-internode length of barley, but, in the case of floral initiation, this same order of change is brought about by less than a tenfold change in energy. 6. The effective pigment absorbed less than one part in one hundred thousand of the radiation incident on an albino barley seedling even in the region of its maximum absorption in the red portion of the spectrum.