Specific Daylength Effects on Leaf Growth and Dry-matter Production in High-latitude Grasses

Plants of Phleum pratense L. cv. Engmo (origin 69° N) andBromus inermis Leyss. cv. Löfar (origin 64° N) raisedin short days gave large and significant increases in d. wt,height and leaf area upon exposure to continuous light, comparedwith 8 h short days, at essentially identical daily inputs ofradiant energy (8 h summer daylight ± low intensity extension).The increases in both plant height and leaf area were causedmainly by increases in the dimensions of the leaf sheaths andblades, which, in turn, were the result of increased cell sizeand number. However, there was a pronounced interaction betweentemperature and daylength such that the greatest photoperiodicstimulation occurred at lower growing temperatures (