Graves: Large Leaf Spot of Chestnut and Oak 173 



should be looked upon as the true Monochaetia Desmazierii. It 

 is probable that Saccardo's smaller measurements were taken 

 from the first lot of material distributed by Desmazieres. With- 

 out going into more detail, it is sufficient for our purposes to 

 state that the correct description of the species is given by 

 Voglino."^ 



The spores make their appearance early in the progress of the 

 'disease, and are borne in dense clusters, or acervuli, which appear 

 to the naked eye as small black dots on the diseased portions, 

 usually on the upper surface of the leaf. In shape the spores are 

 -ellipsoid, and usually divided into five cells, as shown in the ac- 

 companying text figure. The three central cells are large and 

 •dark colored, while the two end cells are small and transparent. 

 Sometimes only two, instead of three central cells appear. At 

 the base of the spore there is a short stipe, 5-10 /x long. At the tip 

 a long flagellum, or bristle, is borne, which usually describes a 

 •curve near its base, and is quite variable in length, 10-25 fx. The 

 average size of the spore, including all of the cells, but omitting 

 the stipe and flagellum, is 20 X 6 ^. 



Successful infection experiments have been carried on with 

 this fungus. Out of a large number of chestnuts sown in the 

 greenhouse early last November, a few germinated in December 

 and later, without waiting over until spring. By the middle of 

 January these furnished fine healthy young trees for inoculation. 

 The leaves were inoculated with the spores in two ways : first, 

 by applying the spores to the surface of the leaf after wetting it 

 with sterilized water, and, second, by wounding the leaves and 

 inserting the spores in the wounded spots. The infections made 

 by the latter method were invariably successful, while the former 

 method did not always cause the disease. On the basis of these 

 results it would appear that wounds from insect bites or mechan- 

 ical causes may probably furnish in nature the starting point of 

 the disease in many cases, and yet there is no doubt that the fungus 

 can enter the leaf without this assistance. It is probable that the 

 age of the leaf has some relation to infection, and investigations 

 along this line are now being carried on. 



' Voglino, P., Sul Genere Pestalozzia. Saggio Monografico. Atti della 

 .Societa Veneto-Trentina di Scienzi Natural! 9-': 7. 1885. 



