STUDIES UPON THE TIME OF FLOWERING OF PLANTS: ANATOMICAL, FLORISTIC AND PHENOLOGICAL ASPECTS OP THE PROBLEM

Abstract

Summary The growing points of more than 100 plant species of diverse habit have been examined between 1937 and 1939, in order to find the exact times of flower initiation. Types of organization for flowering may be classified into (a) direct‐flowering plants, (b) indirect‐flowering plants, (c) cumulative‐flowering plants and (d) climax flowering plants. Initiation of the flower in (a), (b) and (c) may either begin (i) during the period of maximum vegetative growth or (ii) when vegetative growth is at a minimum. In the latter class, any direct cause of flowering operated entirely or largely by external influences, such as those affecting the vigour of photosynthesis, would appear to be eliminated. Abnormal flowering of some indirect‐flowering plants during the autumn of 1938 suggests that their physiological rest periods were concluded at that time. Their normal extension of dormancy until the following spring is probably a direct effect of winter climate. Plant habit, as annual, biennial, perennial, does not appear to affect the time of flowering, unless associated with a store of food, but not all plants with stored food flower early. A series of correlation diagrams of the two variables, temperature and time of flowering, has been prepared from the Royal Meteorological Society's phenological data. These suggest that temperatures before the initiation of flower bud formation, in addition to those at other periods of floral development, may affect the time of flowering. Some species appear to be hastened by higher temperatures than normal at this period, e.g. ivy, and yet other kinds by temperatures lower than normal, e.g. coltsfoot. Flower emergence in thirteen wild plants is hastened by a temperature higher than that of normal climate for a period just before the time of opening.