174 



Mycologia 



Cultures of the fungus have been made on various media. 

 For abundant spore production and vigorous myceHal growth 

 Clinton's^ oat agar gave the best results. Figure i shows a plate 

 culture two weeks old, on this medium. The spores here, in the 

 central darker portion, are extremely dense. For comparison, 

 figure 2 shows a culture of the same age, on potato juice agar. 

 Here only a few acervuli, shown by the black dots, appear. In 

 figure 3 some of the spores produced on the oat agar are shown. 

 They are somewhat larger than those occurring in nature, and 

 also considerably distorted. Figure 5 shows a germinating spore. 



Economic Importance and Control of the Disease 



In some cases, individual trees were observed which had suf- 

 fered a loss of perhaps 40 per cent, of the green assimilating 

 tissue of their leaves as a result of the attacks of this fungus. 

 Usually, however, the damage is much less than this, but always 

 sufficient, it is believed, to cause a considerable diminution in the 

 annual wood increment. Since it appears that this trouble is 

 disseminated over the whole southern Appalachian region, it is 

 one of considerable importance. 



As far as the disease occurs in the forest, very little can be 



done at present to check it. In case of individual trees on private 



estates or in parks, however, the ordinary methods of spraying 



will probably prevent its recurrence. The diseased leaves should 



also be raked up in the fall and burned, as they harbor the fungus. 



spores over winter. 



Yale University, 



New Haven, Conn. 



Explanation of Plate LXIX 



Fig. I. Culture of Monochaetia Desmazierii in oat agar, two weeks old. 

 X §. 



Fig. 2. Culture in potato juice agar, two weeks old. X |. 



Fig. 3. Photomicrograph of spores of Monochaetia Desmazierii Sacc. 

 from oat agar culture. Spores somewhat abnormal, probably due to influence 

 of culture medium. X 275. 



Fig. 4. Photograph of large leaf spot on leaf of chestnut. X §. 



Fig. 5. Photomicrograph of germinating spore of Monochaetia Des- 

 mazierii. X 230. 



* Clinton, G. P., Rep. Conn. Agr. Exp. Sta. for 1909-10. 760. June, 1911. 



