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In a previous paper ) the appearance of the black spore-deposit that accumulated overnight parallel with the perithecium-studded edge of a thick slice of a stroma of Daldinia lying on a horizontal glass plate was discussed. This deposit, instead of being a black line, which would have resulted if the spores were all discharged to roughly the same distance, was in fact a broad band about i cm wide separated from the edge of the stroma by a spore-free region 0.2 to 0.3 cm in width. Further, this band of discharged spores was zoned with two or three darker zones recognizably parallel with the stroma's outline. It was suggested that the spread of the deposit was due to spore projectiles being of all sizes from single spores to groups of eight, since with a given muzzle velocity the distance d of discharge might be expected to increase with the size of the projectile according to the formula d = kr-where r is the radius of the microscopic spherical projectile and k a constant. It was also suggested that zonation might be related to the existence of projectiles of eight definite sizes, although the number of these zones was actually much less than eight.An opportunity for further study of this type of problem was afforded by Sordaria fniicola in which, as in Daldinia, the spores discharged from a single ascus may either remain together or break up into projectiles each of fewer spores. Sordaria has the advantage over Daldinia of a greater maximum distance of discharge (up to 10.5 cm instead of 1.5 cm).Brief reference may be made here to the structure of Sordaria fimicola. The perithecium as seen in longitudinal section has been figured by Hawker (1951) and by von Arx and Miiller (1954), but both their illustrations give a somewhat incomplete picture. Clearly, in the preparation from which Hawker's most accurate figure was drawn, some of the internal tissues were imperfectly preserved, and the illustration of von Arx and Miiller is decidedly diagrammatic. Fig. i, an attempt to present a realistic picture of the perithecium, is based on camera liicida drawings from a number of preparations including sections cut with a freezing microtome from fresh material. The perithecium wall is three-layered, "^fhe outermost layer is composed of cells with relatively thick walls impregnated with melanic pigment, the middle layer of cells free from pigment, and the innermost layer of large and very thin-walled colourless cells. The asci arise from a basal cushion presumably composed in the main of interwoven ascogenous hyphae. In the mature perithecium asci are at all stages of development and no recognizable paraphyses are to be seen amongst them. The little free space within the perithecium is occupied hy slime, not by air. Around the ostiole is a meristematic region by activity of which the neck gradually lengthens during the life of the perithecium. The neck is lined hy delicate and very thin-walled recurved hyphae leaving a narrow canal through which the elongating ascus must push to reach the ostiole.The ascus in S. fimicola, an...