Experiments on the physiology and genetics the smut fungi.—Hyphal-fusion

Abstract

In recent years attention has been devoted to the study of the Smut Fungi, and their cytology is now fairly well known. The results of previous observations on the two Smuts used in the following experiments may be briefly summarised:—The Chlamydospore in both species is uni-nucleate, and on germination a promycelium is formed into which the nucleus passes. There it divides into two, and the two daughter nuclei pass, one to each end of the promycelium, and there divide, so forming four nuclei between which cross walls are then formed (see text-fig. 1, A-E, p. 130). After this stage the behaviour is governed largely by the environmental conditions, either one or more sporidia are budded off from each segment or clamp connections are formed between pairs of segments. (Text-fig. 1, F-G.) No linear order is apparent in these unions, all possible combinations having been observed; and the nucleus and cytoplasm of one segment passes into the other through the clamp connection. Again, no crossing or changing over in position of the nuclei in the unsegmented promycelium has been seen. It has been presumed therefore that the nuclei in the segments, if numbered from the apex, 1, 2, 3, 4, are in pairs, 1 and 2 being the product of one nucleus, 3 and 4 the product of the other. This has been corroborated in the present work.