Studies on the Physiology of Flowering of Timothy (Phleum pratense L.) II. Influence of Daylength and Temperature on Size of the inflorescence1

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Abstract
Inflorescence length in timothy increases when the photoperiod is reduced from 24 to 14½ hours of light; it is also increased by a reduction in ambient temperature from 75° to 55° F. There is a linear relation between total floret number and ear length. Both factors affect ear length by influencing the rate of growth of the spike between spikelet initiation and ear emergence; this implies an effect on either the number of primary spikelet initials or the number of florets produced by branching, or both. Experiments with Lolium temulentum, where daylength and temperature influenced initiation and ear development in a way similar to that observed in timothy, suggest that these factors affect the number of florets at each primary initial. The interrelations of internal and external factors and their influence on inflorescence size in the grasses is discussed.