THE DIFFERENTIATION AND FATE OF THE BRACKEN (PTERIDIUM AQUILINUM) FROND AND THEIR RELATION TO THE AGE‐STRUCTURE OF THE SHOOT AND FROND POPULATION

Abstract

On an acid, dry infertile soil in a frost pocket, there are more short shoots (potential fronds) in bracken than differentiated fronds, and more differentiated fronds than emerge from the soil, and more emergent fronds than live in August. Factors affecting the inception, differentiation and fate of fronds are examined. The inherent tendency of fronds from young shoots to develop and to emerge before those from old renders them more liable to lethal winter and spring frosts and to crippling spring frosts. Drought acts mainly on the late emerging fronds. The normal sequence of emergence may be upset. Through their destruction of reserves and their effect on the means of replenishing them, annually fluctuating frost and drought influence the number of shoots initiated yearly, and hence the age‐structure of the shoot population. A senescent population of bracken is defined as one in which the proportion of young to old shoots is low, and fronds from young shoots to fronds from old is also low. Frost and drought are the causes (not necessarily exclusive) of senescence in this area. Copyright © 1967, Wiley Blackwell. All rights reserved