SPORULATION 317 



formed. Examples of the inhibiting effect of insufficient aeration on 

 sporulation are numerous. Coons (1916) found that lowered oxygen ten- 

 sion inhibited pycnidium formation by Plenodomusfuscomaculans, though 

 there was still sufficient oxygen supply to allow some growth. Leonian 

 (1924) tested the effect of reduced oxygen on pj^cnidium formation by 

 various Sphaeropsidales. This experiment was carried out by culturing 

 these fungi in Petri dishes, some of which were placed in desiccators, while 

 the controls were placed on a table. The following fungi produced fewer 

 pycnidia in sealed desiccators than in the control cultures: Ascochyta 

 tiym'phaeae, Phoma urens, Plenodomus destruens, Phyllosticta opuntiae, and 

 Septosporium acerinum. It is possible that this effect may have been 

 due to the increased concentration of carbon dioxide in the closed vessels. 

 Denny (1933) made an accurate study of the effect of oxygen supply on 

 growth and formation of perithecia by Neurospora sitophila. Only a 

 trace of oxygen was required for limited growth, for it was necessary to 

 keep cultures in the presence of alkaline pyrogallol to inhibit growth 

 entirely. Oxygen concentrations of less than 0.5 per cent inhibited 

 perithecium formation for 30 days, while perithecia formed in air within 

 4 days. This paper should be consulted for the details of conducting 

 experiments of this nature under closely controlled conditions. Some of 

 Denny's data are given in Table 55. 



Table 55. The Effect of Oxygen Concentration on the Formation of Peri- 

 thecia BY Neurospora sitophila 

 (Prepared from the data of Denny, 1933. Contribs. Boyce Thompson Inst. 5, 1933.) 

 Oxygen Cbncentration, % Days Required to 



Form Perithecia 

 20.8 4 



9.4 7 

 3.75 9 



1.5 12 



0.24 None at 30 days 



Conidium production by Choanephora cucurhitarum was poor in tight- 

 fitting Petri dishes (Barnett and Lilly, 1950). Sealing the dishes pre- 

 vented conidium formation, while well-aerated dishes allowed abundant 

 conidial heads to form. Failure to form conidia under these conditions 

 may be due to (1) insufficient oxygen supply, (2) the accumulation of 

 toxic, volatile, metabolic by-products, (3) increased carbon dioxide con- 

 tent, or (4) unfavorable humidity. 



Adequate aeration was one of the most important environmental fac- 

 tors necessary for conidium formation by Piricularia oryzae (Heniy and 

 Andersen, 1948). The cultures emitted a strong odor of ammonia after 

 a few days' incubation. It was believed that aeration removed the 

 ammonia and other volatile metabolic by-products which prevented 



