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THE GARDENERS' CHRONICLE OF AMERICA 
THE 
GARDENERS' CHRONICLE 
OF AMERICA. 
Published by 
THE CHRONICLE PRESS, Inc. 
Office of Publication 
286 FIFTH AVE., NEW YORK 
MARTIN C EBEL, Editor 
EDITORIAL OFFICES— MADISON, N. J. 
Subscription Price, 12 Months, $1.50 
Foreign, $2.00 
Entered as second class matter Nov. 3, 1914, at the Post Office at New 
York, N. Y., under the Act of March 3, 1879. 
Published on the 15th of each month. 
Advertising forms close on the 1st preceding publication. 
For advertising rates apply to 286 Fifth Ave., New York, N. Y. All edi- 
torial matter should be addressed to M. C. Ebel, Editor, Madison, N. J. 
OFFICIAL ORGAN OF 
NATIONAL ASSOCIATION OF GARDENERS 
President, Vice-President, Treasurer, 
W. N. CRAIG, THEO. VVIRTH, JAMES STUART, 
Brookline, Mass. Minneapolis, Minn. Mamaroneck. N. Y. 
Secretary, MARTIN C. EBEL, Madison, N. J. 
TRUSTEES FOR 1916. 
Peter Duff, Orange N. J.; William H. Duckham, Madison, N. J.; William 
Turner, Bernardsville, N. J.; William Kleinheinz, Ogontz, Pa.; John F. 
Huss, Hartford, Conn. 
DIRECTORS. 
To serve until 1917 — Wm. Hertrick, San Gabriel, Cal. ; Robert Angus, 
Tarrytown, N. Y. ; Robert Bottomley, New Canaan, Conn.; Alex. Fraser, 
Newport, R. I.; Arthur Smith, Reading, Pa.; Thomas W. Head, Lake 
Forest, 111.; L. P. Jensen, St. Louis, Mo. 
To serve until 1918— William H. Waite, Rumson, N. J.; William J. 
Kennedy, Chestnut Hill, Mass.; Edward Kirk, Bar Harbor, Me.; John W. 
Johnston, Glen Cove, N. Y.; Carl N. Fohn, Colorado Springs, Colo.; Peter 
Johnson, Dallas, Tex. ; Thomas Proctor, Lenox, Mass. 
To serve until 1919— John W. Everitt, Glen Cove, N. Y.; Thomas W. 
Logan, Jenkintown, Pa., Robert Cameron, Cambridge, Mass.; James Mac- 
Machan, Tuxedo Park, N. Y. ; A. Bauer, Deal Beach, N. J.; David Fraser, 
Pittsburgh, Pa.; George W. Hess, Washington, D. C. 
OFFICIAL ORGAN OF 
AMERICAN ASSOCIATION OF PARK SUPERINTENDENTS 
President, Secretary-Treasurer, 
EMIL T. MISCHE, ROLAND W. COTTERILL, 
Portland, Ore. Seattle, Wash. 
Vice-Presiden ts, 
J. W. THOMPSON, ALEX. STUART, L. P. JENSEN, 
Seattle, Wash. Ottawa, Ont. St. Louis, Mo. 
JOHN F. WALSH, E. P. GRIFFIN, EUG. V. GOEBEL, 
New York, N. Y. East St. Louis, 111. Grand Rapids, Mich. 
Vol. XX. 
July, 1916. 
No. 7. 
LIGHT AND THE LIFE OF PLANTS. 
'IPHE importance of light to the well-being of plants 
is thoroughly understood by gardeners. Daily 
experience shows them not only that plants must be 
exposed to light, but also that if the light which falls 
on the plant be below a certain intensity growth is 
checked. The reason for those facts is also well un- 
derstood by practical growers, who have learned that 
plants recpuire light in order to carry on the manufac- 
ture of their food. Only when light falls on them are 
the green parts of the plant able to construct from the 
raw materials — water and carbon-dioxide, which they 
obtain from the soil and air — the sugar which serves 
as an actual food material for the plant. Whether 
light is also necessary for the manufacture of the more 
complex nitrogen-containing foodstuffs, which the 
plant has also to make for itself, is not so certain. 
\\ hat is certain, however, is that the effects of light 
on plants are by no means confined to this essential 
part in food-manufacture. As is well known, light is 
one of the great directive agents of plants. By its aid 
plants, like animals, find their way. That is to say, 
each leaf and stem and branch contrives to take up its 
proper position as a result of movements of adjust- 
ment in reference to the direction of the light which 
falls on that member. By means of this response to 
light ordinary leaves come to stand at right angles to 
the direction in which light falls on them. 
In yet more subtle ways light affects the fortunes of 
plants. For example, it is well known that if the light 
which a plant receives be of insufficient intensity, al- 
though vegetative growth may continue the plant 
may fail of flower. Although the fact is known, the 
explanation is not. It was suggested long ago that 
light of a certain wave-length (ultra-violet light) plays 
an important part in stimulating the development of 
flowers. Recent discoveries of Professor Loeb suggest 
that this old view may contain something of the truth ; 
for Loeb has shown that the eggs of certain animals 
(sea-urchins) begin to divide when exposed to ultra- 
violet light. 
Another recent discovery which may perhaps lead 
to results of practical importance has reference to yet 
another effect of light on plant-growth. This discov- 
ery concerns respiration, the process whereby the plant 
(or animal), by bringing about the oxidation of its 
own substance — and particularly of the sugars which 
it has manufactured — obtains the energy whereby it 
does the work of living. 
This process of respiration goes on unceasingly night 
and day in both plants and animals ; but it has been 
known for some time that the rate of respiration, which 
is measured by the amount of carbon-dioxide given off, 
is definitely greater during the hours of sunlight than 
during darkness. The most recent investigations have 
yielded what at first sight are remarkable and puzzling- 
results. Thus it has been found that even though a 
plant be kept in absolute darkness (and in a constant 
temperature) the amount of carbon-dioxide given off 
by a plant is greater during the day than during the 
night. The explanation of this curious fact is to be 
sought in the effect of sunlight on the oxygen of the 
air. This effect is termed ionization, and it may be 
likened to that produced by a stonebreaker on a heap 
of stones. In un-ionized air the oxygen is composed 
of unbroken stones (molecules) ; when ionized, the 
oxygen consists of minuter particles which may be 
likened to the broken stones. These minuter parti- 
cles of oxygen combine more readily with the oxidiz- 
able plant substances than do the unbroken molecules, 
and hence the rate of respiration is increased. It 
would appear not impossible that practical advantage 
may be taken of this fact, and that by supplying them 
at night with ionized air the rate of growth of plants 
may be increased. The experiment, so far as we know, 
has not yet been tried, but if the facts described above 
are correct, it is not impossible that "forcing by ion- 
ized air" may become a useful adjunct to the horti- 
culture of the future. — Gardeners' Chronicle {English). 
