62 BULLETIlSr 395, U. S. DEPAETMENT OF AGRICULTURE. 



Moisture favors gi-owth. Desiccation checks growth and favors 

 the formation of chlamydospores. 



The minimal temperature for growth on favorable nutrient sub- 

 strata is less than 2°; the optimal, between 20° and 27°; and the 

 maximal, about 32° C. 



Strong diffuse Ught favors sporulation. 



Normal spores germinate readily in sterile distilled water, rain 

 water, and a large variety of nutrient solutions and agar preparations. 

 The alternate wetting and drying of germinating spores do not 

 appear to be seriously injurious unless the changes are very frequent 

 during the early stages of germination. 



The minimal temperature for germination in water or in a favorable 

 nutrient solution is less than 2°; the optimal, between 20° and 27°; 

 and the maximal, shghtly above 32° C. 



Peach fruit, twigs, and leaves were inoculated with single-spore 

 strains of (Jladosporium carpopMlum from peach fruit, twigs, and 

 leaves, respectively. Each straia produced typical infection upon 

 fruit, twigs, and leaves, with the exception of the leaf strain upon 

 the fruit. In this case the experimental fruits were destroyed by 

 trespassers before the results were available. Each strain of the 

 fungus was repeatedly reisolated and was found to possess the typical 

 morphological and cultural characters of C. carpopMlum. Fruit 

 infection was induced by direct inoculation with scrapings from 

 abundantly spomlating twig lesions. Conclusive positive results from 

 inoculations with C. carpopMlum have not been previously reported. 



Scab infection ordinarily appears shortly prior to the ripening 

 period of early varieties and may continue throughout the season. 



Spore production from fruit, twig, and leaf lesions may begin as 

 soon as infection becomes macroscopic and may continue throughout 

 the development of the lesions. The most abundant sporulation 

 occurs on overwintered twig lesions during the spring and early sum- 

 mer following infection. 



Freshly produced, normal conidia from fruit, twig, or leaf lesions 

 are capable of germinating in sterile distilled water, rain water, or a 

 variety of nutrient media. 



When dry the conidia persist tenaciously upon their sporophores. 

 In water, however, they quickly become detached. Meteoric water 

 appears to be the most important agent in their Hberation and 

 dissemination. 



In the inoculation experiments the period of incubation of the 

 fungus upon the fruit was observed to vary from 42 to 77 days. Upon 

 twigs and leaves it varied from 25 to 45 days. In nature the varia- 

 tions are tmdoubtedly even greater. 



Little natural infection occurs until four to six weeks after the 

 petals faU. Subsequently, under favorable conditions it rapidly 

 becomes more abundant and mav continue throughout the season. 



