W. Robinson 135 



sporangium swells out to form a large apical vesicle into which the 

 undifferentiated contents of the sporangium pass. The zoospores then 

 become defined and are liberated by the rupture of the vesicle. In 

 Phytopkthora, however, no vesicle is formed and the zoospores round 

 off within the sporangium some time before their discharge which 

 takes place directly by the solution or rupture of the apex. In these 

 details therefore the fungus under consideration corresponds to Phyto- 

 phthora and the very large size of the sporangium approximates it to 

 Phytopkthora omnivora (De Bary). Ph. omnivora was described by 

 De Bary attacking a large variety of plants including Clarkia, Gilia, 

 Cleorne, Schizanthus, Fagopyrum, Oenothera, and Epilobium. A number 

 of other investigators have more recently described fungi morphologically 

 almost identical with Ph. omnivora, but owing to differences in the range 

 of hosts which they will attack these have been separated off as distinct 

 species. Examples of species founded mainly upon this physiological 

 distinction are Ph. cactorum (Schenk), Ph. Fagi (Hartig), Ph. omnivora 

 var. arecae (Coleman), Ph. Faberi, and Ph. Syringae (Klebahn). The 

 characters of these various species and their affinities are so completely 

 discussed in recent papers by Pethybridge 1 , Dastur 2 and Butler 3 that 

 a further recapitulation is unnecessary here. In this connection, 

 however, it is of interest that I have already found it possible to infect 

 and to obtain sporangia on seedlings of Gilia tricolor, Ricinus, and 

 Helianthus annuus by inoculation with mycelium from pure cultures. 

 Inoculations upon seedlings of Lepidium, Lyeopersicum esculentum and 

 young plants of Solanum tuberosum gave negative results in all cases. 

 The failure to obtain oospores in cultures or even in infected seedlings 

 of Gilia (in which De Bary found those of Ph. omnivora in abundance) 

 indicates that the aster Phytopkthora is not identical with Ph. omnivora, 

 yet it seems likely that it is a physiological form of it. Further 

 research will show whether the sexual organs are of the character 

 described by De Bary for Ph. omnivora and whether the range of host 

 plants is as wide as in the case of some of the above species. For 

 the present, therefore, the question of the identity of the species of 

 Phytopkthora here described for the first time as producing the wilt 

 disease of asters is deferred ; but this investigation establishes the fact 

 that the causal organism of the disease is a species of Phytopkthora 

 and not a Fusarium as has generally been supposed. It is also clear 



1 Sci. Proc. Roy. Dublin Society, 1913, 1914. loc. cit. 



2 On Phytopkthora parasitica nov. spec, Mem.. T)ep. Agric, India, 1913. 



3 Studies in Peronsporaceae Mem. Dep. Aqric, India, May 1913. 



