Pathogenicity of the Chestnut Bark Disease 53 



noted in about one-tenth of the oldest lesions, and not at all in 

 the youngest lesions. The only evidence secured indicating-that 

 birds really disseminate the spores of the fungus came from a 

 jay. Its feet were washed and the washings upon centrifuging 

 revealed what were apparently a few ascospores. In numerous 

 places pustules were thoroughly picked out by the birds in their 

 attempt to secure the insects. It is quite probable, as in the case 

 of insects, that the viability of any spores found in the excre- 

 ment of birds is destroyed by the digestive fluids while the spores 

 are in the alimentary canal. Fisher (7) states that wind and 

 weather, which carry other forms of disease, are more liable to 

 carry the spores of this disease than birds. 



Heald and Studhalter (9), as a result of extensive investiga- 

 tions conducted in 1913, concluded that pycnospores are carried 

 by birds and that they are brushed off from normal or diseased 

 bark during the movements of the birds over the surface of the 

 bark. The maximum number of pycnospores are carried during 

 the few days following a rain, because at this period they are 

 found in abundance on the healthy bark below the lesions. 



The hauling of diseased logs, cordwood, or bark along public 

 highways or on railroads may carry the spores of the blight to 

 new localities. The shipment and planting of diseased nursery 

 stock is another means by which the disease may be widely dis- 

 seminated. The usual fumigation of nursery stock subject to 

 the disease had no effect on the growth of the fungus. The law 

 creating the Pennsylvania Chestnut Tree Blight Commission pro- 

 vided that nursery stock shipped in Pennsylvania be previously 

 examined and labelled with a distinctive tag by a duly appointed 

 agent of the above-mentioned Commission. 



Germination of Ascospores and Conidia. 



Experiments were conducted on the germination of conidia 

 and ascospores with the idea of ultimately determining their rela- 

 tive importance in the infection of chestnut trees from these 

 sources. Conidia washed into a dish of distilled water were the 

 basis of a series of experiments in which it was found that these 

 spores retained their viability for seven days in this water, but 

 lost it after ten days. If taken out of the distilled water shortly 

 after being washed from the branch and dried for a day they were 

 still capable of germinating. They germinated at once when 

 transferred from the branch to rain water. After germinating 

 in rain water they were unable to resume growth if dried for 

 more than twenty-four hours. Twelve hours drying on a glass 

 slide did not kill them. Pycnidia containing mature conidia were 



