CONTROLLED ENVIRONMENTAL CONDITIONS 291 



salvia flowered with 5, 7, and 12 hours of daily illumination, showed only- 

 incipient flowering with 17 hours, and no flowers at all with 19 and 24 hours. 

 It is a short-day plant. Buckwheat flowered on afl day lengths and pro- 

 duced more dry weight as the day lengthened up to a given day length. 

 The plant grew much more on the longer days with artificial light than it 

 did in the greenhouse when the run was made during March. This is a day- 

 length indifferent plant. The tomato also flowered on all day lengths in 

 which it would continue to grow, but it was soon killed under continuous 

 artificial illumination here used. When given 12 hours a day of artificial 

 iUumination and 12 hours a day of sunlight it did better. The sunlight 

 seemed to balance the injurious effect of artificial light to a degree, but 

 not completely. 



The tomato is especially sensitive to continuous artificial illumination, 

 and geraniums and coleus are likewise much injured by it. Even plants that 

 showed no visible injury in continuous artificial illumination gave indica- 

 tions of incipient injury. Cabbage * increased in weight and carbohydrate 

 content and feU in nitrogen per cent as the day length increased up to 17 

 or 19 hours. With continuous illumination, weight and carbohydrate 

 content fell again and nitrogen percentage increased. Spring wheat and 

 barley showed similar day-length curves in artificial light, and radish 

 showed a continuous increase in dry weight and carbohydrate percentage 

 up to 17 or 19 hours, but a proportional increase was not maintained for the 

 24-hour illumination. Apparently artificial fight alone shows the same 

 day-length effect as daylight or a combination of daylight and artificial 

 light; radishes flowered on long days but not on short days, and in the spring 

 cereals flowering was hastened by long days. The potato showed good 

 tuberization even in continual artificial illumination at 68° F (20° C) but 

 poor under continuous illumination at 78° F (26° C). Tuberization seems 

 to be favored by the joint action of low temperature and long day. The 

 supplemented daylight in the gantry crane house showed similar effects on 

 tuberization. The radish seems to respond readily to increased nitrogen 

 content with abundance of nitrates in the soil and to increased carbohy- 

 drate content with conditions that favor photosynthesis, long day and in- 

 creased CO 2 content of air. With 12-hour illumination and 12-hour daily 

 darkness it has the same composition as on 24-hour alternate illumination 

 and 24-hour darkness; it does not flower in the first case but does in the 

 second. We shall return to a fuller consideration of the chemical compo- 

 sition of plants gro^vn in these rooms after describing the experiments in 

 the gantry crane house and in other special gro\ving conditions, at which 

 time there Avill be evidence for more general conclusions. 



* Cabbage leaves wrinkled and cracked under artificial illumination and the injury- 

 increased with day length. This reaction to artificial hght was partly corrected by day- 

 light. It was also less marked in artificial light of lower intensity, i.e., 350 foot-candles. 

 The authors suggest that the constant direction of the artificial hght rather than the 

 quahty or daily duration may cause the wrinkling and cracking. 



