HELIOTROPISM OF ASCI IN DISCOMYCETES 277 



period of development extends from the initiation of marginal 

 growth to maturity." 



The asci of Ascoholus stercorarius push upwards between the 

 paraphyses and at first are straight. However, shortly before they 

 discharge their spores, they protrude considerably beyond the 

 general level of the hymenium, and their aerial parts bend helio- 

 tropically toward the source of greatest light. Two such helio- 

 tropically curved asci are shown in Fig. 132 in which is reproduced 

 Corner's illustration (arrows added by myself) of a median- vertical 

 section through the whole of a small fruit-body. 1 As in other 



Fig. 132. — Ascobolus stercornriKs, a common copropliilous Discomycete which has 

 heliotropic asci and which puffs audibly. Median-vertical section of a very 

 small apothecium. The apothecium is turbinulate in form ; it was angiocarpic 

 in origin, and tlie primary sheath of cortical cells which overlay a mucilage 

 cavity and the disc feocame ruptured at e e owing to the expansion of the internal 

 tissues, and thus the disc was exposed. The apothecium was built up originally 

 around the archicarp from sympodial clusters of cortical hyphae and paraphyses, 

 the intercalary parts of which now form the medulla. Details of structure are 

 shown as follows : the excipuluin, consisting of the cortex n a and the medulla 

 b b ; c c, the hypothecium (in which the ascogenous hyphae are situated) ; the 

 hymoiium, consisting of asci and paraphyses, above the hypothecium ; d, 

 mucilage ; e e, the broken edges of the primary cortical sheath that at first 

 covered the mucilage cavity and disc ; /, rudimentary paraphyses, evidently 

 forming part of the sympodial clusters of hyphae from which the apothecium 

 was constructed ; g, secondary mycelium composed of hyphae which have growii 

 from the underside of the apothecium as excrescent cortical cells into the sub- 

 stratum ; /;, the archicarp (scoledte) consisting of a bent chain of cells with 

 a wide pore in the centre of each septum ; /, the ascogonium, one of the cells of 

 the archicarp, which gave rise to the ascogenous hyphae ; j, ascogenous 

 hyphae passing upwards through the hypothecium ; k, hooks and hook-cells 

 which were formed at the ends of ascogenous hyphae ; /, young asci pushing up 

 between the paraphyses, each containing a fusion nucleus ; m, an older ascus 

 containing four nuclei ; ;;, an ascus containing eight young spores ; o, an ascus 

 containing eight older spores, each surrounded by jelly ; p, an ascus containing 

 mature or nearly mature spores each of which has a dark-violet cell-wall marked 

 with interlacing white lines and bears on one side a lenticular mass of jelly ; q 

 and r, two highly turgid and fully expanded asci, each containing a thin layer 

 of protoplasm lining the cell-wall, a large central vacuole filled with cell-sap, 

 and massed at the apex eight ripe spores which are about to be violently dis- 

 charged ; the asci q and r protrude beyond the layer of mucilage and their 

 aerial parts are bent heliotropically toward the source of strongest light the 

 direction of which is indicated by the arrows ; when the operculum of the ascus 

 q or the ascus r opens, the elastic ascus-wall will contract and drive out through 

 the operculum not only the eight spores but also a large amount of cell-sap which 

 will be scattered in the air in the form of a fine spray of spherical droplets; 

 s, an ascus which has discharged its eight spores and has slirunk to about one- 

 half of its original volume ; at its apex the hinged operculum can be seen. 

 Drawn by E. J. H. Corner, originally published by him in Trans. Brit. Myc. Soc, 

 Vol. XIV, 1929, but now, with his consent, altered slightly, lettered, described, 

 and reproduced on a larger scale than formerly by A. H. R. Duller. Magnifica- 

 tion, about 340. 



1 E. J. H. Corner, loc. cit., p. 286. 



