OXYGEN, CARBON DIOXIDE, ET AL. 365 



mary of Ingokl (162) has been supplemented more recently by investi- 

 gations of spore discharge in rust fungi (220) and Nigrospora sphaerica 

 (302). With the possible exception of "drop-excretion" discharge in 

 basidiomycetes (50, 51, 52, 229), all these discharge mechanisms rely 

 in some way on either substrate or atmospheric water. We infer that 

 osmotic forces are at work. In immature asci (162) and in the imma- 

 ture active layer of Sphaerobolus spp. (299) glycogen is abundant; its 

 disappearance at maturity suggests that the uptake of water is medi- 

 ated by enzymatic conversion of the osmotically inactive polysaccharide 

 to osmotically active sugars. Such a mechanism, if suitably quantified, 

 might be extended to cover all discharge mechanisms which depend 

 on increasing turgor of a cell or cell layer. 



The elevation of the receptaculum in the Phallales is accompanied 

 by disappearance of glycogen, but in this instance the increase in si/.e 

 may be true growth (58, 95). Elongation of the Agaricus campestris 

 sporophore has been shown to be a growth process rather than simple 

 water uptake (36). 



4. OXYGEN, CARBON DIOXIDE, AND VOLATILE SUBSTANCES 



It is a common observation that sporulation is reduced in closed 

 containers (82, 126, 185) and that submerged mycelium fails to develop 

 spores (84, 201, 321). Although this is usually ascribed to an oxygen 

 deficit, it seems more likely that the accumulation of carbon dioxide 

 is the critical factor. Pyronema conftuens, for example, does not fruit 

 in a closed tube, but if alkali is present to absorb carbon dioxide, peri- 

 thecia develop (248). Carbon dioxide accumulation inhibits the 

 asexual reproduction of Choanephora cucurbitarum (19) and sporo- 

 phore development in Agaricus campestris (181) and Collybia vehitipes 

 (227). 



In large culture containers the sporulation of Piricularia oryzae is 

 dependent upon aeration of the vessel; Henry and Anderson (149) 

 suggest that metabolically produced ammonia is the inhibitory factor. 

 An unidentified volatile substance, probably of microbial origin, in- 

 hibits sporophore development in Psalliota campestris (199). 



The best available data on the oxygen requirement for sporulation 

 are those of Denny (87). Any reduction of oxygen below atmospheric 

 pressure delays the appearance of perithecia. Further, visually esti- 

 mated mycelial growth appeared to be normal at oxygen pressures too 

 low for reproduction. The same phenomenon — a higher oxygen re- 

 quirement for fruiting than for growth — is reported by Ternetz (283). 



