Studies in the morphology of discomycetes: I. The marginal growth of apothecia

Abstract

Summary The sterile tissue of the apothecium consists of two palisade layers, cortex and hymenium, and an intermediate medulla of radial and interwoven hyphae. Marginal growth is performed by a fascicle of hyphae between the cortex and hymenium. Every hypha in the growing-point arises as a lateral, 2–3μ wide, the growth-rate of which rises to a maximum, then falls, the fall being accompanied by branching in the proximal part and maturing of the distal part. The distal parts are transformed on the outside of the growing-point into cortical hyphae, on the inside into paraphyses; the proximal parts form the medullary hyphae. The hyphal system is therefore a sympodium. The growth of the inner hyphae ceases on reaching the surface of the hymenium, but that of the outer hyphae continues for some time at a slow rate: “hairs” are cortical hyphae with a prolonged period of rapid growth. The hymenium is formed at the margin by the apposition of hyphae, the cortex by apposition and outward rotation. Paraphyses are specialised mucilage hyphae which are commonly pigmented. Cortical hyphae have no such pigment and are not mucilaginous; the enlargement of their cells forms characteristically a pseudoparenchyma supporting the hymenium. An explanation of the sympodium at the growing-point is given on the assumption that the apices of the hyphae are fed from the medulla and eventually reach the limit of its nutritional range. Other points in the construction of the apothecium are considered. The hyphal system of the apothecium of Rhizina inflata is exceptional, for it is evidently a monopodium.