[^q8 Journal of Agricultural Research voi. xviii. no. n 



initiating or inhibiting the reproductive or the vegetative phases of 

 development, depending upon whether the plants employed normally 

 require long or short days for these forms of expression. In these 

 experiments a greenhouse 50 feet long, 20 feet wide, and 12 feet high to 

 the ridge, with side walls of concrete 5 feet high to the eaves, was pro- 

 vided with 34 tungsten filament incandescent lights, each rated at 32 

 candlepower, evenly distributed beneath the glass roof. As a control, 

 a similar greenhouse without artificial light was used. The long axis of 

 these houses was on a north and south line. The temperature was 

 approximately the same in the two greenhouses, ranging at night around 

 60° to 65° F. and 75° to 80° during the day. The unlighted greenhouse, 

 however, tended to run two to three degrees higher than the illuminated 

 house. Beginning on November i the electric lights were switched on at 

 4.30 p. m. and turned off at 12.30 a. m., this procedure being followed 

 throughout the course of the experiments. Supplementing the natural 

 length of the winter days with this 8-hour period of artificial illumination 

 has given about 18 hours of continuous daily illumination, approaching 

 in length the summer days of southern Alaska. Under these conditions 

 the following results have been obtained: 



A large clump of Iris florentina L., with all eafth intact, was trans- 

 planted October 20, 191 9, to each of the two greenhouses. The plants 

 exposed to the long daily period of illumination began growing 

 vigorously at once, soon attaining the normal size for this species, and 

 produced blossoms on December 24 and December 30. The controls 

 remained practically dormant and showed no tendency to blossom as 

 late as February 12, 1920. 



Seed of spinach {Spinacea oleracea L.), Bloomsdale Curley Savoy,* 

 was sowed November i, 1919, and came up in both houses on November 

 6. The plants in the control house, 20 to 25 in number, grew very 

 slowly, producing low, compact, leafy growths or rosettes, and gave no 

 evidence of blossoming as late as February 12. The plants in the lighted 

 house elongated very rapidly, soon developing flower stalks, and all 

 blossomed in the period between the dates December 8 and December 

 23. These have continued to elongate more or less, blossoming and 

 shedding pollen continuously, thus becoming in effect " everblooming " 

 plants. 



Seed of cosmos {Cosmos bipinnata Cav.) was sowed November i, 

 1 91 9, and germinated in both houses November 5. In each greenhouse 

 40 to 45 plants were grown. The plants in the control house quickly 

 flowered, and all blossomed in the period from December 22 to Jan- 

 uary 2. The plants in the lighted house grew well but remained in the 

 strictly vegetative stage and were showing no indications of blossoming 

 on February 12. On this date the control plants averaged 30 inches in 

 height and the plants in the lighted house 60 inches. 



• Horticultural variety. 



