SPORE DISCHARGE AMONG ASCOMYCETES 181 



of this mechanism, as it applies to Podosphaera leucotricha, has 

 been confirmed by Woodward [Ingold (1939)]. 



Discharge among other Ascomycetes. It is a matter of com- 

 mon knowledge anions those who have studied Ascomycetes that 

 many species of this class forcibly expel their ascospores [Ziegen- 

 speck (1926)]. Even though this phenomenon has been ob- 

 served in connection with a relatively small proportion of the vast 

 assemblage of widely different species that constitute the Asco- 

 mycetes, undoubtedly most of them will be found capable of 

 such forcible discharge. Many of those who attempt to isolate 

 Ascomycetes in pure culture utilize the phenomenon of expulsion. 

 They have found that the simplest procedure to employ in isolat- 

 ing is to place inverted agar-poured plates above mature perithecia 

 at a suitable height. If favorable moisture conditions are then 

 provided, an abundance of ascospores will be found to have been 

 ejected onto the surface of the agar after a few hours. 



The height to which the ascospores are propelled varies with 

 the species, being governed by the size of the spores or of the 

 spore mass as one of the correlated factors. Hypomyces lacti- 

 fliiorum has been found to shoot its spores to a height of 10 mm, 

 Endothia parasitica, 22 mm, Sordaria fimicola, 60 mm, Podospora 

 fimiseda, 300 mm, and P. curvicola, 450 mm. In P. curvicola 

 Weimer (1917) found that the spore mass of approximately 500 

 spores, held together in a gelatinous matrix, had a diameter of 

 168 to 266 /x and that they were hurled up into the necks of 

 2-liter culture flasks. 



Rate of ascospore discharge. The rate of ascospore discharge 

 from perithecia is controlled by the external factors of moisture, 

 temperature, and light. These factors are interdependent, and in 

 no species does discharge occur unless the water content of peri- 

 thecial tissues approximates the maximum. As may be expected, 

 the output of spores is low at low temperature and increases to a 

 maximum with a rise in temperature. With further increase there 

 is a very rapid decline in the rate of discharge. As far as light is 

 concerned, some species are stimulated by it, such as Nectria cin- 

 nabar'ma and Podospora curvula, whereas others are inhibited, for 

 example, Hy poxy Ion fuscum [Ingold (1939)]. 



For a few species the rate of discharge has been recorded. In- 

 gold (1939) has assembled certain data on this point; they are 

 shown in Table 15. 



