For 30 years botanists have known that plants keep their calendars straight by measuring the length of the day. A spring-flowering plant blooms when the days have reached the right length for that particular species. A fall-flowering plant blooms when the days have got short enough after the summer solstice. Both "long-day" and "short-day" plants can be fooled—by controlled lighting—into flowering out of season.
Last week Drs. H. A. Borthwick, M. W. Parker and S. B. Hendricks of the U.S. Department of Agriculture announced that they had discovered something new about plants' "photoperiodism." They irradiated soybeans and other sensitive plants with narrow-wave...
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