Photoperiodic Responses of Geographical Strains of Andropogon scoparius

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Abstract
40 plants of A. scoparius from 12 points of origin in the U. S. were assembled at the Univ. of Chicago greenhouses in the spring of 1946. The 12 geographical strains represented a latitudinal range of approx. 21 [degree] from Jackson County, Texas, to Price, N. Dakota, and an east-west range from North Haven, Conn., to Cheyenne, Wyo. Their responses to natural day lengths in greenhouse and garden and to constant photoperiods of 13, 14, and 15 hrs. in the greenhouse were investigated. Growth and development were found to be sharply sensitive to length of photoperiod. None of the 12 strains flowered on 13-hr. photoperiod. Plants of only 4 southern strains produced visible inflorescences on the 14-hr. light period. Another strain, from Texas, had initiated floral primordia in this series when harvested on Nov. 1. In the 15-hr. series northern strains produced flowers, but southern strains had not visibly flowered at harvest time, even though culms were elongated. Representatives of nearly all strains produced visible flowers on natural day-length, the southern ones later than the northern. Five southern strains should probably be classed as intermediate-day plants rather than short-day, since they failed to flower on 13-hr. photoperiod and also failed to flower or were delayed in flowering on 15-hr. photoperiod. The northern strains may be long-day plants, since they are able to initiate flowers on long photoperiods but were inhibited from flowering on 13-and 14-hr. photoperiods. With the coming of autumn a state of dormancy was initiated in the 2 series on natural day length; vegetative and reproductive activity ceased in all but the most southern strains. Plants on 13-, 14-, and 15-h. photoperiods remained green, and those in the 15-hr. series continued to produce new elongated tillers. At final harvest, in general, the strains showed a higher percentage of tillers elongated on 15-hr. photoperiod than in the indoor series on natural day length.