When breeders are choosing among unfamiliar varieties as prospects 

 for crossing, they often grow seedlings under different day-length condi- 

 tions to judge suitability for different agricultural regions. One main 

 reason for this country's success in developing and making use of im- 

 proved crop varieties is that breeders have paid close attention to the 

 reactions of candidate varieties to day length. Proportions of light and 

 darkness in each 24-hour cycle are one of the most predictable features 

 of a plant's environment, because they lengthen and shorten in the same 

 dependable pattern year after year. Favorable proportions are so im- 

 portant to some crops that a variety well suited to one farming locality 

 may not be nearly so productive in a latitude as near as 100 miles to the 

 north or south. 



Almost any nurseryman who propagates woody or other plants can 

 nnake good use of photoperiodic principles. And the same is true for 

 any crop grower who tries crossing or other experimental work. 



The woody plants that grow slowly have shown particularly striking 

 responses to light control in recent photoperiodic research. And young 

 trees and shrubs are readily manageable. 



Basic Advantages the Most Important 



Beyond recognized uses --and more could be cited --the technical 

 findings on light -growth relationships are innportant first and foremost 

 for basic knowledge of how and why a plant develops as it does in a given 

 environment. Only when nature's laws and intricate processes are well 

 understood can man hope to adjust agricultural practices to plants and 

 to modify plants to his advantage in a truly scientific way. 



THE USDA ROLE IN PHOTOPERIODIC RESEARCH 



The U. S. Departnnent of Agriculture has worked at photoperiodic 

 research continuously and with an increasing sense of purpose fronn the 

 discovery of the concept. The Agricultural Research Service's Plant 

 Industry Station at Beltsville, Md., has become a world center for pio- 

 neering advances in understanding this phase of plant growth. 



The initial discovery came from a side-line interest of two gifted 

 plant specialists, W. W. Garner and H. A. Allard, whose main task was 

 to deal with tobacco crop problems. 



Although they recognized the importance of their discovery at once, 

 they waited 2 years and learned much more about day length and plant 

 growth before they published their first announcement: A 53 -page 

 account of the photoperiodic concept and their experinaents in a scientific 

 journal. Scientists around the world showed keen interest. Garner and 

 Allard continued this line of study in the Department for about 20 years. 



When the Bankhead- Jones Act of 1935 provided funds for extending 

 basic agricultural research, one prompt action of USDA was to set up a 

 research unit to work entirely on plant growth and light relationships. 



Today, the headquarters for this research at Beltsville are in one of 

 the pioneering research laboratories that the Department established in 

 1957. 



