62 BULLETIN 395, U. S. DEPARTMENT OF AGRICULTURE. 
Moisture favors growth. 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 light 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, slightly above 32° C. 
Peach fruit, twigs, and leaves were inoculated with single-spore 
strains of Cladosporium carpopMlum from peach fruit, twigs, and 
leaves, respectively. Each strain 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 0. carpopMlum. Fruit 
infection was induced by direct inoculation with scrapings from 
abundantly sporulating 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 liberation 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 undoubtedly even greater. 
Little natural infection occurs until four to six weeks after the 
petals fall. Subsequently, under favorable conditions it rapidly 
becomes more abundant and may continue throughout the season. 
