REPRODUCTIVENESS AND SEED GERMINATION 387 



short photoperiod were reduced in size and many were induced 

 to blossom and fruit, while others were unaffected as far as their 

 reproductiveness was concerned. The Biloxi soy bean blossomed 

 in 110 days of 12 hours or in 27 days of 5 hours; and tobacco under 

 similarly changing conditions blossomed in 157 and 58 days re- 

 spectively. It was, therefore, concluded that for each species of 

 plant there is a critical photoperiod essential for fruiting. Those 

 of a short photoperiod, i. e., those which are induced to blossom 

 by daily light periods shorter than 12 hours have been called 

 " short-day" plants, while those that blossom sooner when ex- 

 posed to a photoperiod longer than 12 hours each day are called 

 " long-day" plants. It is, consequently, possible to induce or 

 delay fruiting by exposing or failing to expose the plants to their 

 critical photoperiod. Thus Aster linariifolius, a typical biennial, 

 can be made to complete its life cycle in a few months, and an- 

 nuals such as soy beans, golden rod, and oats can be made to 

 behave like biennials. Tomatoes, lettuce, and radishes are typi- 

 cal " long-day" plants; peppers are "medium-day"; and Salvia 

 and ragweed are " short-day" plants. Buckwheat, on the other 

 hand, is an example of a relatively small group of plants whose 

 reproductiveness is not appreciably affected by the photo- 

 period. 



A very large literature has developed about this subject in the 

 past few years without adding much to the fundamental principles 

 established by Garner and Allard. Auchter and Harley (1924) 

 showed that at time of flowering long- and short-day plants had a 

 similar composition with a high C/N ratio. Zimmerman and 

 Hitchcock (1929) found that long-day varieties of dahlias had 

 fibrous roots (low carbohydrate content) and no accumulations 

 of nitrates; while short-day varieties had fleshy roots (carbohy- 

 drate reserves) and larger accumulations of nitrates in the leaves 

 and stems. The results of these various researches on the chemical 

 composition of short- and long-day plants are not opposed to 

 those of Kraus and Kraybill, but rather are supplementary and 

 show the effect of light in determining the chemical changes within 

 the plant,— changes which are certainly connected with the ratio 

 of the carbohydrates to the other substances present. Since the 

 light is of supreme importance in determining the amount of 

 carbohydrates in the plant, it is not surprising that it should play 

 a prominent part in the processes under discussion. 



