REPORT OF COMMITTEE ON PUBLICATION 137 



zoospores or conidia were carried there through the agency of the rain. It 

 is, moreover, well known that the first spots to appear in the early spring 

 or summer are on the lower leaves. 



Millardet thought that the seedlings growing through the layers of 

 oospores-filled leaves are infected by the zoospores produced in the oospores 

 and the conidia resulting from these primary infections serve as sources 

 of infections upon the surrounding vines. This hypothesis, with the excep- 

 tion of the oospore germination by zoospores, may be tenable in France, but 

 in this country where seedlings never, or at least very seldom, appear in the 

 vineyards, we must search for some other explanation. 



Noack (1899) states that in Brazil the oospores are unnecessary since 

 the leaves are green the year round and the summer stage is constantly 

 present. 



At one time the writer thought that possibly the mycelium of the 

 fungus could hibernate in the roots or canes of the diseased vine and, pro- 

 ducing conidia in the spring, serve as a source of infection. During the 

 auiumn of 1912 roots and canes of certain vines which were known to be 

 badly infected each year were planted in the greenhouse, care being taken 

 not to bring in soil which might contain oospores. 



These vines grew until the following July without any evidence of the 

 mildew, though they were well watered and an attempt made to induce a 

 succulent growth which would probably favor any mycelial development. 



Istvanffi (1913) found the mycelium and conidia within the bud scales in 

 autumn but was not able to prove that a diseased cane or leaves develop 

 from these buds, as Cuboni (1889) thought possible. 



Frechou (1885) states that the mycelium may hibernate in the leaves 

 which do not become moist enough to rot. After five or six months this 

 mycelium may produce conidiophores bearing conidia. He points out that 

 it is extremely rare that there will not be enough moisture during the 

 autumn, winter and spring to rot the leaves, hence this method need hardly 

 be seriously considered. 



During the winter of 1914 the writer had an opportunity to test the 

 possibility of such a method of hibernation. Leaves of a wild vine which 

 were known to have been badly infected, were found in a fine state of 

 preservation, showing no evidence of decomposition and in every way ideal 

 for hibernation of the mycelium as described by Frechou. They were placed 

 in a warm, moist situation, in the hope that conidiophores would be pro- 

 duced but without success, indicating that the mycelium does not hibernate 

 in this manner. 



It is probable that the principal, if not the only, method of hibernation 

 is by means of the oospores. 



After the formation of the first crop of conidia from the primary infec- 

 tions the spread of the mildew becomes much more rapid. The conidia are 

 blown to other vines where they readily germinate if proper conditions 

 exist. The principal factors influencing the germination of the conidia, aside 

 from the presence of moisture are, the temperature, and the proper age of 

 the conidiuin. 



Viala (1893) gives three types of germination of the conidia, namely, by 

 zoospores, by the emission of the entire contents of the conidium and by a 

 germ-tube directly. Istvanffi (1913) also figures the same types and states 



