f
the treated plants.

Unfortunately there is much confusion amid the results of experiments
pertaining to the effects of different rays, including ultra-violet,
visible and infra-red, upon plant growth. If this aspect was thoroughly
established, investigations could be outlined to greater advantage and
efficient light-sources could be chosen with certainty. There is the
discouraging feature that the average intensity of daylight illumination
from sunrise to sunset in the summer-time is several thousand
foot-candles. The cost of obtaining this great intensity by means of
artificial light would be prohibitive. However, the daylight
illumination in a greenhouse in winter is very much less than the
intensity outdoors in summer. Indeed, this intensity perhaps averages
only a few hundred foot-candles in winter. There is encouragement in
this fact and there is hope that a little light is relatively much more
effective than a great amount. Expressed in another manner, it is
possible that a little light is much more effective than no light at
all. Experiments with artificial light indicate very generally an
increased growth.

Recently Hayden and Steinmetz experimented with a plot of ground 5 feet
by 9 feet, over which were hung five 500-watt gas-filled tungsten lamps
3 feet above the ground and 17 inches apart. The lamps were equipped
with reflectors and the resulting illumination was 700 foot-candles.
This is an extremely high intensity of artificial illumination and is
comparable with daylight in greenhouses. The only seeds planted were
those of string beans and two beds were carried through to maturity, one
lighted by daylight only and the other by daylight and artificial light,
the latter being in operation twenty-fours hours per day. The plants
under the additional artificial light grew more rapidly than the others,
and of the various records kept the gain in time was in all cases about
50 per cent. From the standpoint of profitableness the artificial
lighting was not justified. However, there are several points to be
brought out before considering this conclusion too seriously. First, it
appears unwise to use the artificial light during the day; second, it
appears possible that a few hours of artificial light in the evening
would suffice for considerable forcing; third, it is possible that a
much lower intensity of artificial light might be more effective per
lumen than the great intensity used; fourth, it is quite