Evening star., 1950-06-07
Timing in PIont Growth
loid to Blue Pigment
Bosic Substonce Studied
By Federal Scientists
By Thomos Z. Henry

A blue pigment In all plants Is re-
sponSihle for time Of Towering and habit
Of growth. 1t has been determined by
three Agriculture Department scientists
This pigment exists in such minute
quantities that 1t has been impossible 10
isolate the substance by any chemical
means.
II may turn out 10 be one Of the most
basic substances In nature-second only
to chlorophyil. the green pigment IN
leaves which initiates the action Of
photosynthesis and makes life On earth
possible.
Chlorophyll makes Il possible for
plants to use the energy Of sunlight TO
transform carbon and hydrogen into
starches and sugars which are the es-
sential fuels for all higher life. The
newly demonstrated pigment apparently
plays the same role in the phenomenon
Of photoperiodism.
Compared 10 Eye Purple"
It Is compared by Drs. H. A. Borth-
wick. M. w. Parker and s. B. Hendricks
Of the BeltSville Md experiment sta
ton Of the Bureau OF Plant Industry,
to the substance known as visual purple
in the retina Of the eye which makes
vision possible.
While the pigment cannot be ex-
tracted from any higher plant, 1t ap-
pears to be quite similar to q coloring
material found in blue-green algas
which constitute much Of the scum on
stagnant water and are among the most
ancient forms Of life now extant.
1t long has been known that many
plants respond with extreme sensitivity
to the lengths of the periods Of light
and darkness to which they are exposed.
This affects primarily their manner OF
growth. Some grow tall in darkness and
some short. Others behave exactly the
opposite. Similarly. their times of bud
ding and bloSsoming and. consequently,
frulting. are affected
One OF the first discoveries made bv
the Beltsville scientists was that, con-
trary to all previous ideas, the length OF
day in nature or the time OF artificial
illumination In the greenhouse made
no difference. Everything depended ON
the length Of night or unbroken dark
ness.
Growth was unaffected II plants were
darkened during part of the day. 1t
was very notably affected by very brief
periods OF illumination during the night.
Light Bands Studied.
DrS. Borthwick, Parker and Hendricks
then tried to determine what particular
light bands In the suns spectrum were
responsible. They found that the rays
absorbed were red light which is alb
sorbed by certain definite shade Of
blue and that very small amount Of
this specific light could bring about the
effects which had been observed.
There has been some discussion Of an
intensified effort to isolate the elusive
pigment with the hope that crop growth
could be notably affected by injecting
1t into plants.
OF this the Beltsvills scientists are
skeptical. They point out that 1t Is
quite probable that the substance is
necessary only to start off the reaction
which eventually may involve the whole
physiological system of the plant and
that above the minimum requirement.
which must be fantastically low. the
actual amount present would make little
difference. In the same way, they point
out. human vision would not be improved
by increasing the amount of visual pur-
pie in the retina.
ts, Measured by Nature.
Presumably. they believe, the required
amount has been very delicately meas
ured out by nature. 1t acts as a catalyst.
tney pelieVe, TO set into action another
chemical substance. yet to be identified.
which controls time Of Towering.
The same blue pigment. they believe.
may be present in some animals and
be very important in some phenomena
Of animal life. 1t is somewhat similar.
although certainly not identical, with a
pigment known as ptero-bilin which has
been isolated from the wings of cabbage
butterflies. A quite similar material
also Is found in the shells Of some birds
eggs.
Other research has shown the infiu-
ence of day length on reproduction In
some animals. on the time Of moulting
in birds. and on the hair color and fur
quality in mammals. These responses
may all be initiated by the action of
certain red wave lengths of sun light
acting through blue pigment.
There can be little doubt, the scientists
believe. that they are on the trail Of
one Of the most important links between
sunshine and life and one Of the prime
requirements Of life on this planet.