Evening star., 1937-06-26
STARS, MEN AND ATOMS
Notebook of Science Progress in Field,
Laboratory and Study
Laboratory and Study.
BY THOMAS r. HENRY.

A narrow band OF radiation in the
suns spectrum centering around the
wave length Of $500 Angstrom units
may be Of extreme significance in the
phenomena Of terrestrial life. according
to report just issued by the Smith
sonian Institution.
Three years ago DR.. Lewis H. Flint,
then with the United States Depart
ment of Agriculture. made the critical
discovery that the termination of let
tuce seed could be markedly Influenced
by irradiation with light Of different
wave lengths.
The ability Of this seed to germinate.
it was found. was greatly inhibited by
three regions in the spectrum-wave
lengths Of 400. 4,800 and 1000 Angstrom
units. The first two are in the region
OF blue-green light. The last produced
red light on the very edge Of the in
visible mira -red.
Between these two there was a range
covering about 1000 Angstrom units
and including most Of the region of
yellow -orange-red light, where the
ability of the lettuce seed to germinate
appeared to be stimulated. This region
now has been explored systematically
by DR.. Flint. now with the Boyce
Thompson Institute and DIR. E. D.
McAlister OF the Division Of Radiation
and Organisms Of the Smithsonian In
stitution in an effort to locate more
precisely the stimulating influence. They
find that it reaches its maximum close
to the wave length 6700 Angstrom units,
about In the middle of the spectrum
OF red light from the sun.
The Angstrom unit is the measure
most frequently used in stating the
wave lengths of radiation. One of these
units is about 900 600, ,OO0, ,004 of an inch.
1t is not because of the specific abil-
1ty OF light in this region to stimulate
the termination of lettuce seed that
light centering around the 6,700 A. U.
wave length is of particular Importance.
but because of the new insight gained
into the mechanics of plant termination
and growth in general.
The three inhibiting centers in the
light spectrum, it was found, happen
also to be the centers where there is
the greatest absorption of light by the
plant pigment caroline, present in most
plants and also, 1t may be deduced, in
the seeds. These same light bands, 1t
was found, also are most effective in
promoting the strange phenomenon of
phOtotropiSm, or the bending of a
growing plant toward the sun or other
source Of light. This is due to an in
hibition Of growth on the Illuminated
side.
1t aiso happens that the 6700 A. U.
region represents the greatest absorp-
ton Of light by the plant pigment
chlorophyn, which is responsible for
the green color of foliage and is the
''catalyst" by means of which. through
the energy of light, a plant is able to
transform water and the carbon diox-
ide Of the air into its own substance.
Without chlorophyll it is difficult to
see how any life could exist on earth,
since there could be no plant growth,
and plants provide the basic foods for
the animal kingdom.
Now, it appears from these expert
ments, chlorophyll itself can function
only with the appropriate kind of light
which 1t can absorb. The experiments
indicate that chlorophyu Is well as caro-
tine must be present in seeds and that
the termination Of q seed is due, at
least in part, to the activation Of this
substance by the proper wave lengths
OF light.
Says the Smithsonian report: 1.-THE
close analogy between critical wave
lengths of radiation tnf1usnctng seed