Evening star., 1938-10-20
OF STARS,
MEN AND ATOMS
Notebook of Science Prosress
in Field, Laboratory
and Study.
BIZ THOMAS r, HENRY.

~ THOMAS Il. HENRY.
A hormone, formed in the green leaves
Of plants under the influence OF light
and secreted through the plant tissue,
is probably responsible for flowers.
Strong evidence for this hypothesis
is afforded by experiments just reported
to the Soviet Academy Of Sciences from
the governments laboratory OF plant
physiology at Moscow. This hypothe-
tical hormone, florigen, presumably is
the same throughout nature and the
agent alike Of the blooming Of the skunk
cabbage and the rose.
The Russian experiments serve only
to demonstrate the existence Of the
potent chemical substance. No progress
has been made as yet toward its isola-
ton. q step which might have revolu-
tionary effects by making possible the
blossoming Of flowers at any season by
injection Of minute quantities.
In one set of these experiments the
Russian plant physiologist, b. 8. Moskov,
used the Maryland Mammoth variety
OF tobacco. widely grown around Wash
ington. with which Drs. w. w. Garner
and H. A. Allard of the United States
Department Of Agriculture first dis
covered few years ago the phenomenon
Of phototropism, the variations in
growth and blossoming OF a plant with
variations in the length of the day. This
discovery Is described by Moskov as
"one of the most important Develop
ments in biology during the present
century"
Maryland Mammoth forms flower buds
only under short day conditions-day-
light illumination of from 6 to IL hours.
Most varieties OF tobacco, however, will
flower under continuous light. Moskov
grew the Maryland Mammoth under
perpetual light in a Moscow greenhouse,
a condition under which, as previous
experiments has shown, it could not
possibly flower. Then he cut of the
tops Of his plants, and grated on in
their place tops Of another variety Of
tobacco, closely related but which blooms
under continuous light.
A fair proportion Of the plants sur
vived this major operation, he reports.
Within five days new shoots began to
appear on the Maryland Mammoth
stems which budded and bore flowers,
still under continuous illumination. The
Mowers were characteristic Of the Mary
land species rather than of the species
used as graft.
In this group" Moskov reports, "all
the plants floWered, while not q single
plant f1oWered in any Of the other groups.
Thus it may be considered established
that flower producing substance passed
from the leaves of the scions to the side
shoots OF the mammoth stock and in
duced these shoots to flower under the
influence Of continuous light"
Similar results were obtained by graft
ing OF sunf!owers on Jerusalem arti-
chokes, but in this case 1t was the graft
which was induced to bloom by hormone
secreted from the plant to which it was
attached.
In his report to the Soviet Academy
Moskov presents evidence to show that
only the leaves are concerned in the pro-
duction Of this hormone. The rate Of
production under the stimulus Of light
Is governed by the hereditary character
OF the plant. In some 1t Is formed very
rapidly and is responsible for the flood
OF blossoms in spring. In others, as the
tobacco plant, the production rate is
quite slow and there is evidence that
when there is too much light and in
hibitory secretion is set up, as In the
case of the Maryland Mammoth.
Moskov sums up the conclusions from
his experiments as follows:
The hower-producing substance is
synthesized by the leaves Of mature plants
which previously have passed through
ctnr -
ment.
"The leaves of some so-called Short
day species synthesize this substance
only under conditions OF definite, opti-
mum variations Of light and darkness,
while leaves Of other species also syn
thesize 1t under continuous illumination.
"Flowering Of varieties differing In
their phototropic reaction is conditioned
by one and the same flower producing
substance, irrespective of whether it is
synthesized by leaves of a short-day or
q long day variety. Consequently leaves
Of short-day plants under conditions of
a short day and Of long day plants under
conditions of long day synthesize one
and the same flower producing sub
stance.
In order that this flower producing
substance be transferred from the scion
to the stock a very Weak union of their
external tissues is sufficient. Hence it
may be assumed that this substance Is
conveyed within the plant not by the
usual channels but directly from cell to
cell by osmotic processes.
utilizing the fiower-producing sub
stance of mature plants by different
kinds of gratis and various injections,
one can rely on success in accelerating
the Towering of seedlings of woody
species"