May 1. 1920 Philippine Downy Mildew of Maize 113 



ties representing the several types of maize and teosinte and in sorghums^ 

 under all the various conditions of the wet, dry, and transitional periods 

 of the year. Furthermore, infected plants have been subjected to various 

 changes in temperature, moisture, light, aeration, and soil, in the attempt 

 to induce the formation of such structures. So far, all efforts have been 

 in vain, and, although facilities were not available for any such experi- 

 ment as subjecting the infected plants to long-continued cold or total 

 freezing such as might occur in our own com belt, still the experiments 

 which were made seem to indicate that the formation of resting bodies 

 by the fungus in maize occurs very rarely if at all under the conditions 

 naturally encountered in the Philippine Islands. 



The possibility that the conidial stage may be restricted to maize while 

 the production of oogonia takes place on some other host invites con- 

 sideration. As has been mentioned above, the writer has found a Scle- 

 rospora attacking a common field grass, Saccharum spontaneum, in this 

 region; but whether this fungus, of which only the oogonial stage has 

 been seen, is in any way connected with the conidia-bearing Sclerospora 

 on maize remains to be determined. 



IDENTITY OF THE CAUSAL FUNGUS 



The important question of the identity of this Philippine Sclerospora 

 necessitates a comparison with the other members of the genus. Since 

 our knowledge of the Philippine form is at present confined to its conidial 

 phase solely, no comparison is possible between it and those species of 

 which only the oogonial Stage has been recorded, such as the remarkable 

 Sclerospora magnusiana Sor. (20) of Equisetum from Russia, the rare 

 Sclerospora farlowii Griff. (7) of Chloris from western North America, 

 the recently described Sclerospora miscanthi T. Miy. {14) of Miscanthus 

 from Japan, or even the more common Sclerospora macros por a Sacc. {8), 

 which is widely distributed on a large number of grasses and even has 

 been found on the tassels of maize in Italy. Likewise, the type species 

 Sclerospora graminicola (Sacc.) Schroet., although known from all over 

 the world on a wide range of wild and cultivated grasses and even 

 recorded on maize in Argentina {21), can not be directly compared, 

 because the conidial stage, even though known, is rare and is character- 

 ized by the germination of the conidia by zoospores and by the invariable 

 predominance of the typical oospores. 



A far closer relationship is shown between the Philippine form and 

 those Oriental species which occur on maize or related gramineous hosts 

 and are characterized by the partial or complete lack of an oogonial 

 stage, with the concomitant predominance of the conidial phase, which 

 is distinguished further by the germination of the conidia by tubes. 



Of these there have been enumerated the following: Sclerospora 

 javanica (Rac.) Palm, of Java (originally described by Raciborski as 

 Peronospora maydis); Sclerospora maydis (Rac.) But., of India; and 



164177—20-^2 



