246 RESEARCHES ON FUNGI 



ascospores in a mature upright apothecium (Fig. 116, p. 240) are 

 all inclined slightly upwards. This is well shown in Fig. 120, A. 



A mature ascus, such as the one shown in Fig. 119 at b, is turgid 

 owing to the high osmotic pressure of the cell-sap contained within 

 its great central vacuole, and its thin elastic cell-wall is stretched 

 like that of a toy balloon blown up with air. When the ascus 

 explodes, it opens at its apex by means of a hinged operculum 

 (Fig. 119, c), but the aperture is formed not symmetrically about the 

 longitudinal axis of the ascus as in most other Ascomycetes, but 

 obliquely on one side of it. Moreover, as shown in Fig. 120, B, the 

 aperture so formed always looks upwards toward the mouth of the 

 apothecium. In the light of these facts, we can readily perceive 

 why it is that the ascus does not shoot its spores in the direction of 

 its long axis and why, when puffing takes place, the spore-cloud is 

 projected straight forward from the mouth of the apothecium in a 

 direction parallel to the apothecium-axis. A comparison of Figs. 116, 

 118, B, and 120 will make all this clear. 



When an ascus explodes, the elastic cell-wall wliich has been 

 distended by the osmotic pressure of the cell-sap contracts with 

 considerable force and great rapidity, in consequence of which the 

 ascus shortens and becomes thinner. The ascus-apex is di'awn down 

 to the level of the paraphyses (Figs. 119, c, and 120, B) and no 

 further, so that the total shortening of the ascus as a whole is only 

 to the extent of about one-sixteenth of its original length or about 

 6* 3 per centl An ascus, when shooting out its eight spores one after 

 the other, is continuously contracting in length. If, before all its 

 spores had been discharged, its apex were to be drawn down below 

 the external surface of the hymenium as defined by the paraphyses, 

 it is clear that the remaining spores could not be discharged properly ; 

 they would strike against the paraphyses and so never get into the 

 air. It is thus seen that the shortening of an exploding ascus by 

 an amount just equal to what at first protruded and no more is a factor 

 in the organisation of the apothecium which makes for success in 

 the dispersion of the spores. When an ascus explodes, its diameter 

 becomes reduced to about three-quarters of what it was originally. 

 Therefore the ratio of the circumference of a turgid ascus to that of 

 the same ascus after explosion is about 100 : 75 ; or, in other words, 



