364 



PHYSIOLOGY OF THE FUNGI 



(1948) that the amino acids leucine, lysine, and proline favored spore 

 germination in mutants of Neurospora deficient for those amino acids, it 

 also seems likely that spore germination in certain vitamin-deficient fungi 

 may be aided by the addition of the vitamins in question. A careful 

 study of the effects of vitamins is needed. 



The spores of some fungi, such as Botrytis cinerca, germinate much 

 better Avhen in contact with plant tissue than in distilled water (Brown, 

 1922). It was concluded that certain substances diffuse out of the host 

 plant into the infection drop containing the spores and stimulate germina- 

 tion and infection. Leach (1923) believes that a similar situation may 



100 



80 



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o 



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§ 40 

 I 

 20 



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pH of medium 



Fig. 75. The effect of the pH and kind of medium on the percentage of germination 

 of spores of Lenzitcs sacpiaria at 20 to 23°C. A, in sugar-beet decoction; B, in 2 per 

 cent bacto-peptone sohition; C, in Czapek's full nutrient solution. (Redrawn from 

 Webb, Ann. Missouri Botan. Garden 8: 325-327, 1921.) 



exist with Colletotrichum Undemuthianum. The spores of this fungus 

 germinated poorly in distilled water alone, but distilled water plus a 

 piece of fresh bean tissue gave a high percentage of germination. Fresh 

 bean juice was equally effective, but boiled bean decoction did not stimu- 

 late germination. However, green-bean agar made from a similar decoc- 

 tion gave excellent germination, as did potato-dextrose agar. These 

 results led Leach to conclude that two distinct stimulating factors may 

 be involved. A portion of Leach's data is summarized in Table 61. 



Some know^n stimulants may eliminate the need for certain factors 

 ordinarily supplied by natural media for the germination of spores of 

 Phycomijces (Robbins et al., 1942). Germination of spores was about 

 12 per cent or less on mineral-dextrose agar with thiamine. The addition 

 of an extract of potatoes, or of other natural products, of hypoxanthine, 

 acetate, or some other organic acids increased germination to nearly 100 

 per cent. Treatment of spores with aqueous pyridine had the same 

 favorable effect. These authors believe that certain factors (called Z 

 factors) are essential in spore germination. One of these (factor Zi) 



