EFFECT OF THE EELATIVE LENGTH OF DAY 

 AND NIGHT ON FLOWEEING AND FRUITING 

 OF PLANTS. 



By W. W. Gakner and H. A. At.t.ard, 

 Physiologists, United States Department of Agriculture. 



[With 17 plates.] 



One of the marvels of nature is the transformation of the green, 

 growing shoot of the plant into the blossom, closely followed, as a 

 rule, by the appearance of the fruit. As everyone knows, flowers 

 are to be found in an endless variety of shape, size, and color, and 

 the fruits which follow are equally varied in form and color. Those 

 who systematically observe this profusion of form and coloration 

 in flower and fruit are almost led to conclude that nature has pretty 

 well exhausted the possibilities, even if no account be taken of the 

 countless numbers of plant forms appearing in the past which, for 

 various reasons, were unable to maintain the struggle for existence, 

 having been lost in the process of evolution leading up to the plant 

 world of to-day. Another striking feature of flowering and fruit- 

 ing is that each species as a rule reaches these stages of development 

 at certain definite periods of the year, so that the flowering of cer- 

 tain plants comes to be closely identified with each of the seasons. 

 On the other hand, there is no single season in which plants as a 

 whole flower and fruit. Some are in flower and maturing fruit 

 during every month of the year, except possibly under extreme con- 

 ditions of climate. Again, some plants flower and fruit within a 

 few weeks after the seed germinate, while others may require 25 or 

 50 years or even longer to attain the flowering stage. Moreover, it 

 is well known that the general type of vegetation, including various 

 features of flowering and fruiting, undergoes marked changes as one 

 proceeds northward or southward from the Equator. Finally, it 

 often happens that transfer of a given species northward or south- 

 ward leads to important changes in its usual flowering and fruiting 

 habits. 



It seems unnecessary to dwell upon the fact that the development 

 of flower and fruit is of the greatest importance to the plant, for in 

 many instances, particularly in the large group known as annuals, 



