PLANT LIGHT-GROWTH DISCOVERIES. . . 

 From PhotoperiodismTo Phytochrome 



Getting out of living plants a chemical that triggers their growth 

 changes, from seed to fruiting, has brought us closer to a new era in 

 agriculture- -a time when nature's naechanisms will be understood well 

 enough to avoid many of man's uncertainties over what to expect of a 

 planted crop. 



When the U. S. Department of Agriculture announced this break- 

 through achievement in September 1959, the news introduced a new nanne: 

 phytochronne, from Greek words meaning plant color. Scientists in the 

 US DA Agricultural Research Service coined the name to fit a chemical 

 they had detected in plants in the early 1950's, and can now separate 

 from plants and examine in almost pure form. 



The chemical, a light-sensitive blue pigment, is so tiny in amount 

 that it gives no tinge of blue to a growing plant's color. Yet reaction of 

 the blue substance with the sun is potent and direct. Light and darkness 

 have other roles in the life processes of plants. But phytochrome's 

 go -stop signals direct a plant's progress from one stage to the next as 

 if a master valve were operating. 



Revelations of phytochrome's existence and workings give new 

 meaning to discoveries that began in 1918, when two USDA scientists 

 learned that some plants wait for short days to form seed. They also 

 found that plants differ in the day lengths that lead to seed formation, 

 flowering, and other transitions in a life cycle. The discoverers coined 

 a name for their new-found principle of growth: photoperiodism, to 

 mean "the response of organisms to the relative length of day and night." 



Light -growth discoveries have far-reaching importance for farmers, 

 florists, gardeners, and, in fact, plant growers everywhere. A science- 

 minded public may be expected to take increasing interest in this space 

 relationship of the sun and earth's plants. 



HOW LIGHT-GROWTH KNOWLEDGE SERVES AGRICULTURE 



Since all plant growers deal with some specific plant in its environ- 

 ment, fragments of photoperiodic knowledge have been put to agricultural 

 uses almost from the time the initial discovery was reported in 1920. 



Florists First in Commercial Crop Application 



Florists were the first commercial growers to take interest in 

 technical aspects of photoperiodic science to improve their crop manage- 

 ment for tinned markets. For nearly 40 years, they have controlled 

 day -night length with artificial light and shades of opaque cloth. 



They know that expected bloonaing of some flower crops can be 

 thrown off if night is not a complete blackout. Even a street lannp near 

 a greenhouse has been known to delay a poinsettia crop from blooming 



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