736 



ELECTRO-HORTICUL TURK. 



were divided between the two houses. Those in the 

 light compartment were from 15 to 18 feet from the lamp, 

 in rather weak light. The first bloom appeared just four 

 weeks after the starting of the light, and in the light 

 house. For a month or six weeks thereafter the lighted 

 plants bloomed more profusely ; but at that time the dark- 

 house plants began to surpass the others, both in num- 

 ber and size of flowers and vigor of plants. In other 

 words, the lighted plants bloomed earlier, did not make 

 such stocky plants, and they soon exhausted themselves. 

 It is possible that they would have endured longer if 

 they had been established in the beds for a longer period 

 before the light was put upon them. 



When do the Plants Grow ? — It is thought that 

 plants grow mostly at night, using the material which 

 they have manufactured during the hours of sunlight. 

 The question then arises when the lighted plants grew. 

 Did they grow more rapidly than the others during the 

 fewer hours of darkness, or did they grow when the 

 electric light was burning ? We have made many tests 

 with auxanoraeters — instruments which measure and re- 

 cord the periodical growth of the plants. The most im- 

 portant fact which these readings have shown is that let- 

 tuce-plants, under normal conditions, grow about as 

 much in daylight as in darkness ; and the periodicity of 

 growth was very irregular. Lettuce-leaves were found 

 to grow more rapidly in the light house for the first 

 week or so, at which time growth became greater in the 

 dark house. That is, the leaves matured more quickly 

 under the light. 



SUMMARY. 



I. The influence of the electric arc-light upon green- 

 house plants is greatly modified by the use of a clear 



glass globe or the interposition of a glass roof. Plants 

 which are much injured by a naked light may be bene- 

 fited by a protected light. 



2. As a rule, plants are earlier under the electric 

 light than when grown in ordinary conditions. 



3. The light can be suspended above the house with 

 good effect. 



4. Lettuce is greatly benefited by the electric light. 

 An average of five hours of light a night hastened ma- 

 turity from a week to ten days, at the distance of ten 

 and twelve feet. Even at forty feet, in only diffused 

 light, the effect was marked. The light appeared to in- 

 jure young newly transplanted plants. 



5 Radishes were also benefited by the light, but not 

 to a great extent. When the light was hung in the house, 

 however, whether naked or projected by a globe, radishes 

 were injured. 



6. Beets and spinage appeared to be slightly benefited 

 by the light. 



7. Cauliflowers under the light tended to grow taller 

 than in ordinary conditions, and to make fewer and 

 smaller heads. 



8. Violets and daisies bloomed earlier in the light 

 house. This corroborates results obtained with other 

 flowers in our earlier experiment. 



g. The electric light does not appear to determine or 

 modify the hours of growth of lettuce and some other 

 plants which have been studied in this particular. Plants 

 which are benefited simply grow more rapidly during 

 the customary period. 



10. I am convinced that the electric light can be 

 used to advantage in the forcing of some plants. — 

 L. H. Bailey, in Bulletin 42, Cornell Exp. Station. 



