FIXATION OF SPORES IN THE ASCUS 245 



apex. 1 De Bary 2 in this connection said, " Similar apparatus may 

 perhaps frequently be in use especially in the Pyrenomycetes. ... In 

 many cases, especially in the Discomycetes, there is no such apparatus 

 present, the spores being suspended in the fluid of the ascus. The 

 spores must have nearly the same specific gravity as the fluid; 

 if not, they would change their position as the ascus changes its 

 inclination, which they do not do. Most, if not all, spores produced 

 in asci sink in pure water; the fluid contents of the ascus must 

 therefore be of greater specific gravity than pure water, since it 

 holds in suspension bodies of greater specific gravity than water. 

 If increase in the amount of the fluid contents causes the apical 

 portion of the ascus to stretch more than the other parts, currents 

 must be set up in the fluid in the direction of the apex and continue 

 as long as the expansion continues, and push the spores therefore 

 permanently towards the apex. The arrangements of the spores 

 may then be affected by special directions in the currents which 

 we cannot at present determine, as well as by the conditions of 

 space noticed above." This hypothesis of currents does not seem 

 to me to be at all adequate to explain the position of the ascospores 

 at the end of the ascus. There are various objections of a physical 

 character which may be made to it, but it does not appear necessary 

 to discuss them. On the other hand, I shall show that in Peziza 

 repanda the position of the spores is attained by other than hydro- 

 static means. 



In Peziza repanda the eight spores occupy a subterminal 

 position, so that there is a short space between the first spore and 

 the ascus lid (Fig. 79, C and E). Schroter 3 has figured an ascus 

 of P. repanda with the first spore in contact with the lid. This 

 arrangement may often be seen in dead asci but never in living 

 ones. Each spore possesses a firm cell-wall, and in addition is 

 coated on one side with a thin oval gelatinous investment 

 (Fig. 79, E). These investments appear to serve the purpose of 

 attaching the spores to one another so that they cannot slip 



1 Zopf, Sitzsber. d. Berliner naturf. Freunde, Feb. 17, 1880. Cited from de Bary's 

 Comparative Morphology and Biology of the Fungi, etc., English translation, 1887, p. 88. 



2 De Bary, loc. cit. 



3 J. Schroter, " Pezizinese," in Die naturlichen Pflanzenfamilien, by Engler and 

 Prantl, Teil I., Abteil. 1, p. 183, printed 1894. 



