IV. Investigations on the abnormal outgrowths or intumescences on hibiscus vitifolius, linn.— a study in experimental plant pathology

Abstract

The peculiar pathological outgrowths termed intumescences are found on the leaves and young shoots of plants of various kinds. Those referred to in the following pages occur so regularly on Hibiscus vitifolius, Linn., in the glazed forcing pits of the Cambridge Botanical Gardens, that they might easily be, and have been, regarded as normal growths. In 1898-99 Professor Marshall Ward called attention to the probability that they are really abnormal and pathological, and I undertook their investigation to test the point. The first part of the work concerned their anatomy and development, and it was shown that they are chiefly hypertrophied out­ growths of epidermal cells, beginning at a stoma. The protrusion and division of the epidermal cells result, in the typical case, in the formation of a chimney-like outgrowth, singularly like the neck of the archegonium of a fern, and bearing the raised-up stoma at its apex. (Fig. 1, p. 164.) The cells of this intumescence—a term which distinguishes them from the normal hairs of the plant, and which were also examined—are highly turgid, and give a peculiarly glistening appearance to the intumescence, so that a leaf densely covered with them appears as if covered with water glands like an ice-plant. They vary much in size and in numbers, hut it soon became apparent that they are very apt to predominate on plants in the moist warm atmosphere prevailing in the houses at certain seasons. No trace of minute insects, or fungi, or parasitic organisms of any kind, were found in connection with them.