in time for Christmas. Home-grown poinsettias may similarly fail to 

 keep a Christmas blooming date if some house lamp cuts their dark 

 hours too short. 



Florists in the South have extended artificial lighting to outdoor 



acreages of autumn and winter chrysanthemums, where a cash return 



per square foot would justify the cost- -to delay flowering for timed 

 markets. 



Field Crop Growers 



Outdoor light control may always be too expensive for much use on 

 field crops. But farmers can make good use of photoperiodic knowledge 

 in other ways --to outwit some adverse growing conditions, for example. 



When rains prevent planting on schedule, some crops can be planted 

 several weeks late and still catch up well enough to mature a crop. 

 Soybean progress is so strictly controlled by day -length changes that 

 a succession of plantings even of the same variety tends to mature only 

 a fe-w days apart. 



Photoperiodic knowledge was a national asset in World War II when 

 rainy spring weather in 2 years threatened much-needed soybean pro- 

 duction. Farmers who thought it hopeless to try for a belated crop were 

 reassured by plant scientists that they had time to get a worthwhile yield. 

 Production per plant might be smaller than if sowing had been at the 

 best time. 



Knowing that some crops shift growth stages in close step with the 

 sun gives farmers a wider choice of planting dates in favorable weather, 

 as well as emergencies, to gain some advantage. They can time the 

 planting of certain crops to minimize weed competition, or to allow for 

 more vegetative growth by a forage plant. 



Some of the newer knowledge of what light does in launching seed 

 germination may help farmers eventually to fight weeds in a new way. 

 Such use of light depends on technical findings explaining conaplex rela- 

 tionships of light, temperature, moisture, and other environmental con- 

 ditions. But with enough knowledge, it may become practical to induce 

 weed seeds to sprout all at once underground, and then destroy them 

 quickly with chemicals. 



Experimental Growers and Nurserymen 



Plant breeders and other experimenters control light as the florist 

 does, indoors and out, and in more varied ways. 



Day -length management enables breeders to bring different varieties -- 

 with different photoperiod requirements - -to bloom simultaneously for 

 crossing. It enables them also to grow more generations of seedlings 

 a year, thus providing new varieties faster for farmers' needs. These 

 techniques have served plant breeders since 19^2, when they found that 

 in one season they could grow two crops of some wheat varieties in a 

 greenhouse and still have time to add a third crop in the field. 



