EFFECT OF LIGHT ON PLANTS GARNER AND ALLARD. 575 



For these experiments a much larger dark house was constructed, 

 special provision being made for ventilation without admission of 

 light. A series of steel tracks, each entering the dark house through 

 a separate door, was provided ; and on these tracks were placed a 

 number of trucks arranged for supporting the test plants in their 

 containers. In this way each series of plants could be conveniently 

 transferred into the dark chamber and out again as often as desired. 

 A general view of the dark house and the steel trucks bearing the 

 test plants is afforded by plate 3. In these later tests four varieties 

 of soybean differing in time of maturity were used, as follows : Man- 

 darin, flowering and maturing early in the summer ; Peking, somewhat 

 later than Mandarin; Tokyo, rather late in flowering and maturing; 

 Biloxi, a very late variety, as already pointed out. In addition to 

 the Maryland Mammoth, another commercial variet}^ of tobacco 

 known as Connecticut Broadleaf and a variety of Nicotiana i^ustica 

 were used in the experiments. The former results were fully con- 

 firmed and also were considerably extended. When allowed to re- 

 ceive only 12 hours of sunlight daily Biloxi soy bean planted in May 

 and early June was in blossom within four weeks after germination, 

 whereas the control planting out of doors did not begin to flower 

 till about the second week in September or nearly four months after 

 germination. Similarly, the Tokyo flowered in about 25 days when 

 exposed to 12 hours of light daily, while the control plants began 

 to bloom in August, about 65 days after germination. The Peking 

 blossomed in about three weeks under the 12-hour exposure and the 

 control plants blossomed during the latter part of July, about 50 

 days after germination. The Mandarin flowered in three weeks 

 under the 12-hour light exposure and in four weeks under the full 

 summer length of day. It is perfectly clear that the later the va- 

 riety of soy bean in maturing the greater is the effect of the arti- 

 ficially shortened day-length in hastening the appearance of flowers. 

 This, of course, is just what would be expected if the decrease in 

 length of day as fall approaches is really responsible for the fact that 

 the period between germination and flowering of late varieties is 

 progressively shortened as plantings are made later and later through 

 the summer. In other words, late varieties will not flower and fruit 

 till exposed to shorter days than occur in midsummer. 



The Maryland Mammoth tobacco when exposed to 12 hours or 

 less of sunlight daily behaved just as it did in the earlier experi- 

 ment. The Connecticut Broadleaf and the variety of Nicotiana 

 rustica used in the test, however, did not show any decided response 

 to the shortened length of day. It thus appears that the Mammoth 

 tobacco, like the late varieties of soy bean, will not flower and fruit in 

 midsummer, as a rule, because of the excessive length of the day., 

 The effect of shortening the day-length is shown in plate 5. 



