Growth and Nutrient Responses of Little Turkish Tobacco to Long and Short Photoperiods.

Physiological studies of strongly photoperiodic species in lonig alnd short day have hitherto dealt predominiantly with the effect of day length upon development rather than uponl growth. In photoperiodic species which flower in only one of two contrasted day lengths, it becoiles difficult to compare or interpret data on growth due to simultaneous developmental differences of plants grown in unlike photoperiods. The use of so-called dayneutral species whose flowering response is relatively independent of day lenigth facilitates recognition of growth as opposed to developmental responses caused by the photoperiod. Though data are available on the photoperiodic responses of certain day-neutral forms such as the tomato, it nevertheless seemed worthwhile to undertake a study of growth responses of a species having a distinetlydifferent structural habit from those types studied heretofore. Preliminary tests with Little Turkish Tobacco, a dwarf form of Nicotiana tabacun, revealed that vegetative growth and flowerinlg were both fairly uniform over a wide range of day length. It was found possible to maintain approximate developmental similarity and date of flowering of Little Turkish Tobacco in dav lengths as short as six and one-half hours on the one hand and as long as fourteen hours on the other. The ontogenic eele thus appeared to be comparable over wide photoperiodic ranges even though differences in photoperiod produced certain contrasts in general growth habit. In order to determine the structural and metabolic effects of differences in day lenigth, the developmental eyele of Little Turkish Tobacco was traced from the early vXegetative to the fruiting stage in long and short days respectively. Methods