SPORE GERMINATION 365 



has been identified as hypoxanthine, while the identity of factor Z2 i» 

 still unknown. An explanation of the effects of these stimuli is given by 

 these authors: 



The dormant spores are considered to lack sufficient available Z factors for 

 germination. The extracts of natural products or the Z factors furnished in the 

 medium supply this deficiency, which may also be met by treatment with heat, 

 cold, acetate or pyridine. These treatments are thought to change the Z factors 

 in the spores from an unavailable to an available form. 



The effects of certain gases and volatile compounds upon germination 

 have also been demonstrated. It has been observed that spores of num- 

 erous fungi germinate better in a container in which some living plant 

 part is also present. This was demonstrated for Basisporium gallarum 

 by Durrell (1925), who also found that the introduction of carbon dioxide 



T.^ELE 61. The Effect of Various Media and Plant Tissues on Spore Germina- 

 tion OF Colletotrichuni lindemuthianum 

 (Leach, Minn. Agr. Expt. Sta. Bull. 14, 1923.) 



Medium Germination, % 



Distilled water 3-6 



Sucrose-nitrate (Czapek's) solution 5-11 



Sucrose-nitrate (Czapek's) solution plus bean decoction 10 



Bean decoction 8 



Distilled water plus fresh bean tissue 83-95 



Distilled water plus sunflower tissue 5 



Distilled water plus wheat tissue 12 



Distilled water plus corn tissue 10 



Distilled water plus tomato tissue 2 



Sucrose-nitrate (Czapek's) solution plus bean tissue 95 



Green-bean agar 97 



Potato-glucose agar 98 



into the container enclosing the spores gave the same increase in germina- 

 tion. The same effect was demonstrated for Ustilago zeae (Platz et at., 

 1927). An atmosphere containing 15 per cent carbon dioxide was found 

 to be optimum for spore germination. Such a condition gave a pH of 

 the medivmi from 4.9 to 5.6. These authors conclude that the stimulating 

 effect is apparently due to "a definite action of carbonic acid." Is it 

 possible that this is an example of heterotrophic utilization of carbon 

 dioxide? 



While the release of carbon dioxide into the atmosphere by various 

 living plant parts may explain the stimulation of spore germination in 

 many cases, the presence of carbon dioxide alone will not explain certain 

 results obtained by some workers. For instance, spore germination of 

 Botrijtis cinerea was stimulated by the presence of living tissues of apples 

 or leaves of Ruta or Eucalyptus in the same container, while tissues of 

 potato tuber and onion scales inhibited germination (Brown, 1922). 



