456 Report of the Mycologist op the 



microscopic examination of the interior of the leaf reveals mi- 

 nute fungus threads (hyphse) running through the cells. These 

 fungus threads cause the cells to turn brown and die. 



The second fungous disease makes its appearance a little later 

 in the season. The leaves are affected in about the same manner 

 as in the Septoria disease, but in this case the naked eye can 

 see that the surface of the leaf (on both sides) is covered with 

 small pustules (sori) containing a brown powder. Some of the 

 pustules are considerably darker colored than others. Under 

 the microscope the brown powder is found to be composed of 

 the spores of the fungus, Puccinia Helianthi S. The light-brown 

 pustules contain uredospores and the dark-brown pustules 

 teleutospores. (Figs. 4 and 5, plate XXXII.) The uredospores 

 are capable of germination as soon as they are mature, and are 

 the means by which the disease spreads from leaf to leaf and 

 plant to plant. The teleutospores require a period of rest before 

 germination. Most of them probably do not germinate until the 

 following spring. It is their oflQce to carry the fungus over the 

 winter. This fungus, like the Septoria fungus, has a mycelium 

 which grows within the tissues of the leaf and derives its nour- 

 ishment therefrom. The Puccinia is a true rust. 



Both the Septoria and Puccinia inhabit other species of Hcli- 

 anthus. Particularly is this true of Puccinia, which has been 

 found on almost every known species of HcUanthus. 



The Septoria disease can probably be prevented by the use of 

 any of the ordinary fungicides, but the rusts are difficult to com- 

 bat. 



The HoRSE-CnESTNUT Disease. 



The horse-chestnut, Aesculus Hippocastanum, is a common 

 shade tree on Long Island. In July the leaves begin to show 

 brown spots, which continue to enlarge and coalesce until 

 finally the entire leaf is brown and dead. Long before frost 

 the foliage is disfigured, the affected leaves begin to fall, and 

 people wonder what is the matter. 



There are several causes which may produce this condition, 

 but the chief offender is a parasitic fungus, Phyllosticta sphaerop- 



