The Concept of Minimum Leaf Number

Abstract

SUMMARY Several quotations of minimum leaf numbers for floral initiation are given in the literature, but it was thought desirable to obtain further evidence that they do represent, as claimed by Purvis and Gregory for rye, obligatory vegetative growth preceding the attainment of Klebs's Bliihreife. The effects of mineral starvation on leaf number, as in Purvis's original experiments, were therefore tested with Xanthium, Eupatorium adenophorum, and Celosia argentea. In each of these, near-constant leaf numbers are characteristic of plants induced to flower rapidly by continuous short-day treatment. In each, treatments such as starvation which retard vegetative growth do somewhat reduce the numbers. In Xanthium indeed, the concept of Bliihreife is superfluous, for the 8 leaves to be accounted for could be explained as the primordia present in the seed plus the extra leaves initiated during daylength induction. For the other two plants, on the other hand, the sum of these is still many short of the required number, and for them a con cept of Bliihreife expressed by leaf number is retained, but with the admitted doubt whether all factors controlling their flowering are yet known. Klebs in 1913 invented the term 'Bliihreife' for a postulated stage in the development of a plant signifying its 'ripeness' for environmental conditions to induce flowering. It is evident that he could not himself characterize the stage, save by the negative criterion that none of the environmental variants at his command would induce initiation in rosettes of Sempervivum funkii before the end of the summer.