Photoperiodism in the Plant Kingdom

Abstract

THE announcement of the formative effect of such a dilute factor as relative length of day and night, introduced by Garner and Allard¹ as photoperiodism, has become the subject for many studies by ecologists and physiologists. Although different investigators hold divergent and conflicting views as to the exact class even of forms and races within a species, not to speak of the class of distinct species, there seems to be a general consensus of opinion as to the existence in the plant kingdom of three categories or groups of plants in respect of the so-called photoperiodic response or photoperiodic adaptation. The existence, however, of the very large neutral group which possesses no clearly defined critical photoperiod² might almost alone indicate the invalidity of that classification; but the fundamental fallacy lies in the study of photoperiodism as an isolated episode, without any reference to the preceding (including seed ripening) and subsequent periods in the life-history of the plants.