24 



RESPONSE OF PLANTS TO ARTIFICIAL LIGHTS 



the other hand, showed small leaves and less fruit 

 under these conditions. 



The most favorable results, however, were secured 

 in the case of lettuce, when the house was lighted 

 only half the night (Fig. 44). At the end of three 

 weeks the lettuce plants under the influence of 

 electric light were fully 50 per cent in advance of 

 those in the normal house, and the color and other 

 characteristics of the plants were equally good. 

 The lighted plants had received about 70| hours 

 of electric light during this period, and they were 

 ready for the market one month later ; but it was 

 six weeks before the plants in the normal house 

 were equally developed. This forcing required 

 161J hours of electric light, at a cost amount- 

 ing to about $7. This experiment was repeated 

 several times, with practically the same results. 

 Further experiments showed that the injurious 

 effects of electric light can be overcome by the 

 interposition of glass, and good results were ob- 

 tained by suspending a lamp surrounded by a 

 globe. Plants that were injured by the naked arc 

 light hung inside the house, were benefited by the 

 same light hung above the roof. Experiments were 

 also made with colored screens. The practical con- 

 clusions which Bailey drew from his researches are 

 that lettuce can be profitably forced by the use of 

 the electric light, and that probably many fiowers 

 can be similarly benefited. 



Bailey's experiments with other market-garden 

 crops and flowers under glass gave varying results 

 which, on the whole, were not encouraging, the 

 light in some cases not producing much modifica- 

 tion, while in others modifying them in an unde- 

 sirable way. Some of the unfavorable results which 

 he noticed were a spindling growth, a bleaching of 

 some of the leaves, disintegration of the cells and 

 a collapse of the chlorophyll bodies ; but these 

 injuries are lessened or prevented by the inter- 

 position of clear glass, which cuts off the ultra- 

 violet rays. 



W. W. Rawson, a Boston market-gardener, has 

 employed electric light for some years in connec- 

 tion with his lettuce business, and has reported 

 beneficial results from the use of an arc light sus- 

 pended over his houses. 



Bonnier, of the University of Paris, has investi- 

 gated extensively the effects of electric light on 

 plants and has arrived at many interesting con- 

 clusions which are not at variance with those of 

 other experimenters. He found that electric light 

 contains more of the ultra-violet rays, which can 

 be screened out or weakened by the use of thick 

 glass, and that plants illuminated by screened 

 electric light differed widely from those cultivated 

 normally, as well as from those cultivated under 

 an intermittent light, — twelve hours of darkness 

 and twelve of light. According to his observations, 

 plants grown entirely under electric light possessed 

 much greater quantities of chlorophyll, and even 

 the deeper-lying tissues not normally possessing 

 chlorophyll were green. The axes of plants we're 

 also shorter than those grown under normal con- 

 ditions, the leaves smaller and thicker and the 

 flowers normally developed but more highly col- 



ored. The internal structure of such plants 

 strongly resembled etiolated plants ; that is, the me- 

 chanical tissues were not well differentiated. On 

 the other hand, he found that plants exposed to 

 discontinuous electric light showed some abnormal 

 symptoms, but, in general, they possessed similar 

 characteristics to plants grown in sunlight. It is 

 thought that an uninterrupted duration of illumi- 

 nation is responsible for the deviation from the 

 normal structure. 



Bonnier made comparisons with plants grown in 

 northern latitudes and those grown on the moun- 

 tains of central Europe, and he maintains that the 

 plants of northern latitudes possess less differen- 

 tiation of structure than those in the mountains of 

 central Europe, and that the same species of plants 

 grown in continuous light resemble those which 

 are found in the polar regions. 



Electric incandescent light. 



Rane experimented with incandescent light, the 

 results of his work appearing in Bulletin No. 37 of 

 the West Virginia Experiment Station. His results 

 appear to be very similar to those secured by Bailey 

 and others with the arc light. 



The essential difference between the arc light 

 and the incandescent light in this connection is 

 that In the arc light the chemical or actinic rays 

 are prominent, while in the incandescent light these 

 are only slightly present. The spectrum of the in- 

 candescent light is that of carbon at low intensity, 

 the luminous part of the lamp being cellulose ; it 

 is modified somewhat by the glass of the bulb. The 

 incandescent light is much steadier than the arc, 

 and it casts no sharp shadows ; it is less expensive 

 and requires almost no care. Rane found 



( 1 ) That the incandescent electric light has a 

 marked effect on greenhouse plants. 



(2) That the light appears to be beneficial for 

 some plants grown for foliage, such as lettuce. 

 The lettuce was earlier, weighed more and stood 

 more erect. 



(3) That flowering plants blossomed earlier and 

 continued in bloom longer under the light. 



(4) That the light infiuences some plants, such 

 as spinach and endive, to run quickly to seed. 



(5) That proper watering appears to be more 

 important with radishes, beans and cuttings than 

 improper watering plus the electric light. 



(6) That the stronger the candle-power the 

 more marked the results, other things being equal. 



(7) That most plants tended toward a taller 

 growth under the light. 



Acetylene light. 



The use of acetylene light for forcing plants has 

 not yet had sufficient study to justify positive 

 assertions regarding its value. Perhaps the most 

 important investigations were those made at the 

 Cornell Experiment Station in 1905 and 1906, and 

 reported by John Craig, in the " Acetylene Journal " 

 for September, 1906. The following discussion is 

 an abstract from this report. (The full report, in 

 bulletin form, to be made by the Cornell Station, is 

 not published as this article is written) : 



