47 



number of hours of daylight. Correspondmgly, the early summer 

 flowers and crops must have a longer period of daylight. This 

 has been proved as to a large number of plants, and the scientists 

 believe that the principle will hold throughout the higher forms 

 of plant life, and that it is probably applicable to animal life as 

 well. 



Reproduction Depends on Day Length 



The plant can not attain sexual reproduction, it has been 

 shown, except when it is exposed to a favorable length of day. 

 The requirements, however, differ widely with species and var- 

 ieties. But a length of day that is unfavorable to reproduction 

 may be favorable to growth. Under that condition, the plant 

 continues its vegetative development profusely and indefinitely 

 without bearing fruit. A length of day may be found that is 

 favorable both to sexual reproduction and vegetative growth. 

 That tends to bring about the "ever-bearing" type of fruiting. 



By employing dark chambers to shorten the period of light 

 and artificial lights to extend it, scientists of the Department 

 have shortened or lengthened the life cycle of plants, have made 

 some of them complete two cycles in a single season, have 

 brought others into flower and fruit months in advance of their 

 regular time and, with still others, have greatly delayed and even 

 completely prevented fruiting. 



Long series of tests have been made with soy beans, tobacco, 

 wild aster, climbing hempweed, beans, ragweed, radish, carrot, 

 lettuce, hibiscus, cabbage, violets, goldenrod, spinach, cosmos, 

 iris, beggartick, buckwheat, and various other plants. 



A test made with Biloxi soy beans will show how the principle 

 works. For the test plants the day was shortened by several 

 hours. That is, they were exposed to the light only from lo 

 o'clock in the morning till 3 o'clock in the afternoon. They 

 were first placed in the dark house on May 20. Control plants, 

 otherwise treated exactly like the test plants, were left exposed 

 to the light from dawn till dark. The first blossoms appeared on 

 the dark-house plants on June 16. No blossoms appeared until 

 September 4 on the plants that were left in the light all day. 

 But the dark-house plants averaged only 6 or 7 inches high, while 



