HiuKA: Stödif^ on SoMr Downy Mxde.vs of Agricultural Plants 155 



begin to show a discoloured appearance, then soon slirivel and die out. It seems 

 to be a noteworthy fact tliat, wlien a young seedling was once affected, its 

 subsequent leaves are infected in succession by the hyphac which extended 

 through the tissue. The conidia and conidiophores on the lower surface of 

 the mature green leaves are conspicuous and easily recognizable at a glance. 

 So far as the writer's observations are concerned, they are produced night after 

 night on the same leaves during three weeks or more. 



3. In the field, the viability of the conidia is lost as soon as the dew 

 dries up. The viability of the conidia, collected before sunrise and brought 

 in the laboratory which was kept at 24°C. and humidity 75°^, is mostly lost 

 after 20 minutes, while the viability of them kept in the moist condition is 

 prolonged far longer. Indeed, dryness is fatally injurious to the conidia. 



4. As the mode of conidial germination is very significant in the taxo- 

 nomy of the fungus under consideration, a special attention was paid on it. 

 As a rule, the conidia germinate by the liberation of zoospores, but a few by 

 sending out germ-tubes. This latter mode of conidial germination, howe\'er, 

 is found more freqnently at high temperature or in a prolonged moist condi- 

 tion. To a certain extent, the both types of germination are reversible to each 

 other. After a careful observation, the writer came to the conclusion that the 

 mode of germination by zoospores is the typical, because the conidia ger- 

 minated by germtubes were generally so small in number that they might be 

 al.njjt negligible from th; taxonomic stand-point. 



Botanical I,abr)ralory, 



Imperial College of Agriculture, 



Gifu, Japan 



