235 



Another series of tests Avas made by covering -well-establislied plants in the beds. 

 A tight box, 18 inches square and 1 loot high, was placed over certain plants during 

 the daytime, and was removed at night and placed over contiguous ])lants of tlic 

 same kind. Thus one sot of plants received only electric light and one only sun- 

 light, and inasmuch as both were covered during half of the twenty-four hours, any 

 error which might have arisen from the covering itself (as lack of ventilation and 

 increased heat) was eliminated. February 7 certain radishes in the light house 

 which had been planted 2 weeks were covered. In 8 days some of the plants which 

 were covered during the day were dead and the remaining ones were very weak. 

 At the same time those which were covered during the night had made a better 

 growth than they had before, and better than contiguous plants which had not 

 been covered. An examination of the leaves of the plants receiving only the 

 electric light showed th^t they contained no starch and verj' little or no chlorophyll. 

 February 8 two lots of beans and radishes were planted in pots sunk to their brims 

 in the soil between the radish rows in the light house. One lot was covered during 

 the day and the other during the night, as above. Germination was the same in 

 both lots. February 25 the daylight beans had made a stocky groAvth of 3^ to 4 

 inches, while the electric-light lot had made a weak growth of 8 to 9 inches. Rad- 

 ishes behaved in a similar manner. March 3 the leaves of the electric light beans 

 began to wither, and both beans and radishes were dead March 10. The daylight 

 lots continued to grow thriftily. 



Similar experiments with plants of German ivy {tSe^iecio saxndens), 

 carnation, begonia, and peas also showed the injurious efiects of the 

 electric light. 



The above experiments show conclusively that within the range of an ordinary 

 forcing house the naked arc light running continuously through the niglit is injuri- 

 ous to some plants; and in no case did we find it to be profitable. But the fact that 

 the light hastens maturity or seed bearing suggests that a modified light may be 

 useful under certain conditions. 



Experiments with a protected light running all night. 



Early in March, 1890, an ordinary white opal globe was placed upon the lamp, and 

 for 5 weeks experiments similar to those already described were conducted. The 

 effect of the modified light was much less marked than that of the naked light. 

 Spinach showed the same tendency to run to seed, but to a much less extent, and the 

 plants were not afl^ected by proximity to the lamp. Lettuce, however, was decidedly 

 better in the electric light house. Radishes were thrifty in the light house and the 

 leaves did not curl, but they produced less than in the dark house, although the dif- 

 ferences were much less marked than in the former experiments. These second series 

 of experiments can scarcely be compared with the former ones, because of the greater 

 amount of sunlight which the plants received in the lengthening days of spring. 

 The figures obtained from radishes, however, may afiord a practically accurate com- 

 parison because of their rapid growth. 



The following flgnires represent the average weightin ounces of radishes 

 in the light and dark houses, respectively : Entire plant, 0.29 and 0.33 ,• 

 top, 0.12 and 0.11 ; tubers, 0.17 and 0.22. The percentages of marketa- 

 ble tubers were 89 and 94. 



The loss due to the electric light averages from 1 to 5 per cent in the different 

 comparisons, while the loss occasioned by the naked light was from 45 to 65 per cent. 

 It is also noticeable that while the tops or leaves were lighter under the naked 

 light, they were heavier iiiidtr tlie niodilicd light than those of uorinal plants; an<l 

 this is iuteresting in eoiinectiou with the fact that lettuce did better umh'r the 

 iwodified light than in the dark house. « * * 



