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 possible that some other efficient light-source may be more effective in forcing the growth of plants. These and many other factors must be carefully determined before judgment can be passed on the efficacy of artificial light in reducing the cost of living in this direction. Certainly, artificial light has been shown to increase the growth of plants and it appears probable that future generations at least will find it profitable to use the efficient light-producers of the coming ages in this manner.