RESPONSE OP PLANTS TO AETIPICIAL LIGHT 



25 



The chief interest in the use of acetylene light 

 for forcing plants, centers about the fact that in 

 its composition it more nearly resembles sunlight 

 than any other artificial illuminant in use. It is 

 composed of the same colors and in very similar 

 degrees of intensity. Miinsterberg makes the fol- 

 lowing comparison of color values of acetylene and 

 sun rays, allowing 1 to equal the value of each 

 color af sunlight : 



Sun 

 Red 1 

 Yellow 1 

 Green 1 

 Blue 1 

 Violet 1 



Acetylene 

 1.03 

 1.02 

 .71 

 1.46 

 1.07 



Indigo and orange are not given. The ultra-vio- 

 let rays, the injurious factors in the case of electric 

 light, are practically absent in acetylene, although 

 blue and violet are equally strong. 



In these experiments, acetylene was added to 

 sunlight, being turned on after twilight. For com- 

 parison, the experiments were conducted in warm 

 (60°-65°), medium ' (50°-55°), and cool (45°-50°) 

 rooms. Lettuce, parsley and spinach were hastened ; 

 coleus increased in vigor ; asparagus showed little 

 effect ; begonias gave increased growth, but delayed 

 flowering period ; Cobcea seandens produced 15 

 to 20 per cent more vine ; ferns, leeks, onions 

 and beets showed very little effect ; radishes in the 

 cool house in the dark days of autumn produced 

 more than twice the root product, the time period 

 was increased 62 per cent, and the maturing period 

 shortened about 20 per cent ; strawberries grew 

 more vigorously and ripened fruit sixteen days 

 earlier ; peas and bush beans were benefited ; pole 

 beans produced a much heavier vegetative growth, 

 but matured fruit later ; cucumbers were appar- 

 ently injured. 



The results of the experiments may be briefly 

 summarized. Comparing the results of the differ- 

 ent vegetables, we find 



(1) That with the exception of the cucumbers,, 

 all the forms had a decided increase of the foliage 

 parts. 



(2) That the time of fruit-maturing is variously 

 affected, the strawberries and peas maturing ear- 

 lier, the tomatoes and pole beans later, and the 

 cucumbers and other forms practically unchanged. 



(3) That there is, as a rule, an increase in the 

 amount of fruit, also in size of individual fruits, the 

 cucumber being the chief exception. 



(4) That the chief beneficial effects of the light 

 are to make up for deficiency of sunlight, to give, 

 with few exceptions, stronger and more vigorous 

 top growth, and to help overcome unfavorable con- 

 ditions in certain other lines. 



(5) That there seems to be a limit in rapidity of 

 growth, beyond which plants cannot be forced at 

 all proportional to the attendant expense. Just 

 what conditions govern this limit or where the 

 limit is in forcing-house plants, is as yet unknown. 



Photosynthetic processes are completed to the 

 point of starch-making ; root systems increased in 

 the main proportionately with top development. 



Influence on blooming. — With three exceptions, 



all plants bloomed earlier under acetylene light 

 than under sunlight. Some of the geranium plants 

 bloomed twenty days earlier. The blooming of car- 

 nations was hastened, but the stems were elongated 

 to an injurious extent. The growth of Easter lilies 

 was increased 

 and the flower- 

 ing period has- 

 tened (Fig. 45). 



The influence 

 on the quantity 

 of the bloom- was 

 marked. In 

 every case there 

 was an increase, 

 two or three 

 times as many 

 blossoms being 

 produced in 

 some plants. The 

 effect on the 

 duration of the 

 bloom was some- 

 what contradic- 

 tory. Cucumber 

 flowers remained 

 on the vines a 

 shorter time. 

 Lily and narcis- 

 sus flowers lasted 

 longer under the 

 acetylene. Bulb 

 plants came to 

 maturity tunder 

 acetylene light 

 alone with no 

 sunlight, and 

 other plants 

 made green foli- 

 age (Fig. 46). 



General sum- 

 mary. — These 

 preliminarytests 

 gave marked results, but much more experimental 

 work must be done. Ninety to ninety-five per cent 

 of the plants experimented with responded favor- 

 ably to the stimulus given by the acetylene light. 

 There was no uniformity of results within a group 

 of related plants. No striking detrimental results 

 were observed except when plants were grown 

 under optimum conditions. 



Incandescent gaslight. 



L. C. Corbett experimented with the Welsbach 

 incandescent gaslight, the results of his work ap- 

 pearing as Bulletin No. 62, of the West Virginia 

 Agricultural Experiment Station. These tests were 

 of an economic rather than a scientific nature. In 

 no case was the artificial light found to be a satis- 

 factory substitute for daylight. But it is thought 

 that, could the conditions of the plants in the dark 

 chamber during the day be kept as nearly normal 

 as are the conditions for plants exposed to the arti- 

 flcial light at night only, the results would be very 

 different. A possible explanation of the stimulus 



Fig. 45. Lily grown only in svtnllglit, 

 at the tight; a plant of equal 

 strength and age grown with 

 acetylene light in addition to sun- 

 light, at the left. 



