Studies on the Pathological Anatomy of the Hypertrophied Buds of Camellia japonica caused by Exobasidium Camelliae

Abstract

The present paper deals with the writer's investigation on the histological changes of hypertrophied buds of the camellia (Camellia japonica L.) caused by Exobasidium Camelliae SHIRAI.
The hymenium of the causal fungus forming a continuous layer over the whole surface of the deformed buds develops at first in the intercellular spaces of the cortex and is covered with 2 to 25 layers of cells under the epidermis (Plate, 1, 2, h). These subepidermal layers of cells rupture and then break into a number of small pieces, exposing the hymenium. Both hypertrophy and hyperplasia of cells take place in all the affected parts and consequently the proper arrangement of cells is changed. In the portion of leaf in the deformed buds, no trace of distinction between palisade and spongy parenchyma is found. Epidermal cells and subepidermal cells of cortex covering the hymenium of the causal fungus expand in the tangential direction, but the cells of cortex under the hymenium elongate radially (Plate, 1, 2). This arrangement of the pathological cells is similar to that described by the writer in his previous paper (1) on the white rust of rape. He recognized it to be osmomorphosis.
The new formation of vascular bundles, resembling the cortical bundle in some respects, is found in cortex (Plate, 1, b). The cambium is formed at first in the cortex along the original phloem portion (Fig. 3) and the formation of xylem or phloem portions occurs from this cambium. The newly formed bundles are usually collateral or bicollateral, but sometimes they consist of leptocentric or hadrocentric structure (Fig. 4, 5 and Plate, 3, 4). They extend obliquely towards the hymenium, and the tracheal elements are also recognized at the ending of these bundles near the hymenium. The connection of the new bundles with the original bundles seems to serve for the nutrition-supply of the host to the causal fungus. In 1903 HOUARD reported the formation of the similar bundles in an insect gall and he called them “faisceaux d'irrigation”.