Phyllomorph Senescence in Streptocarpus molweniensis

Abstract

Examination of the phyllomorph of Streptocarpus molweniensis establishes that notwithstanding its cotyledonary origin and continued growth from a basal meristem, it has a fairly typical leaf anatomy. The most unusual feature is the seasonal senescence and loss of the distal 60 per cent of the lamina. This is accompanied by direct development from the mesophyll of a senescence boundary of phellem. There is no predetermined abscission zone. This type of senescence is a means of perennation, whereby the meristem is safeguarded against a depletion of nutrient and water reserves. The phyllomorph presents a system very suited to the study of the initiation and control of senescence and abscission. It is proposed that cytokinin distribution has a primary role in this respect.