COMPARATIVE RESPONSES OF LONG-DAY AND SHORT-DAY PLANTS TO RELATIVE LENGTH OF DAY AND NIGHT

Abstract

The primary purpose of the present discussion is to contrast the behavior of the so-called long-day and short-day types of plants in terms of their response to differences in length of day and to consider the problem of satisfactorily classifying plants into these two groups. In the first paper by GARNER and ALLARD dealing with the effect of length of day on plant growth, published about 12 years ago, two broad facts were brought out with respect to initiation of sexual reproduction, namely: (1) that some plants are more sensitive than others to the length-of-day factor; (2) that of the more sensitive group some respond to relatively long days while others respond to relatively short days. Thus we have one group embracing what may be designated as the indeterminate type of plant and a second group which can be conveniently divided into the long-day type and the short-day type. This classification has proved helpful and it seems desirable that it be retained, at least until some better system is devised. It appears, however, that unless a better understanding can be reached as to the basis on which the classification rests, considerable confusion is likely to result. In dealing with the action of length of day on plant growth, greatest interest naturally attaches to its formative effects, and in the writer's own studies the action of the light period in initiating or suppressing sexual reproduction has been stressed. It is on these effects that our classification of plants into long-day and short-day groups is based. In a recent general review of photoperiodism in plants, SCHICK2 suggests that for those plants in which tuber formation is of importance, this reaction to the light period rather than flower formation be used as a basis for classification, and this