SECRETARY’S REPORT 91 
If bean seedlings are simultaneously exposed to monochromatic 
red and far-red radiant energy, the growth response elicited is deter- 
mined by the energy ratio of the two sources. The red response is 
dominant, even up to ratios of 1 to 10, although at this ratio the 
response is only 50 percent of that produced by red used alone. 
The interaction of gibberellin, kinetin, and cobalt with the photo- 
process has been studied and evaluated. The results indicate that 
there is no direct interaction between red irradiance and the added 
substances, although all these materials do exert a modifying influence 
on the final growth response. These reactions were assayed by the 
measurement of the opening of the stem hook of young Black Valen- 
tine bean seedlings, which has been shown to be a quantitative deter- 
mination of the growth response. 
Dr. John B. Wolff and Leonard Price continued studies on the 
effects of radiant energy on the biosynthesis of protochlorophyll in 
leaves of higher plants grown in the dark. A single exposure to a 
saturating irradiance of red or blue energy converts most of the 
protochlorophyll present in the dark-grown leaf to chlorophyll a. 
Subsequently, protochlorophyll is resynthesized in the dark from 
precursors present in the leaf, but during the first 2 or 3 hours this 
process is very slow. Later, the rate of synthesis gradually increases. 
The experimental procedure followed was to expose the leaves briefly 
to monochromatic energy, then incubate in the dark overnight, and 
next test for their ability to resynthesize protochlorophyll. It was 
found that red energy near 650 my» is more effective than an equal 
quantity of blue energy near 445 my in stimulating the rate of proto- 
chlorophyll resynthesis. These wavelengths were selected because 
they are at the maxima of the action spectrum for the photochemical 
conversion of protochlorophyll to chlorophyll a. If the red irradia- 
tion is followed immediately by a treatment with far-red energy be- 
tween 710 and 730 my, the stimulatory action due to red energy can 
be largely nullified. The far-red energy by itself had little effect on 
pigment synthesis. 
In a study of the biochemical changes involved in the development 
and maturation of the chloroplast of higher plants, some progress 
has been made in the isolation of intact proplastids from dark-grown 
leaves. In excised leaves which had been irradiated with red energy, 
both the protein concentration and dry weight of the isolated plastid 
fraction were found to have increased over those of etiolated leaves, 
but the protein had increased more rapidly than the dry weight. 
Studies are now in progress to determine the conditions for biosyn- 
thesis of plastid components, with emphasis on the carbohydrate 
energy sources required for such syntheses. 
