212 AGRICULTURAL EXPERIMENT STATION. [Jan. 



leaves of the star cucumber, because its conidial threads 

 are developed in large numbers from each of a number 

 of closely situated leaf pores. The structure of the 

 spore-bearing threads in the two species is strikingly dif- 

 ferent, and furnishes the essential means of distinguishing 

 between them. The details of this structure and the chief 

 differences may best be understood from Figs. 11 and 15. 

 Correlated with the development of small haustoria is fre- 

 quently found, as in the grape-vine mildew and in P. 

 australis (Fig. 15), a pinnate branching of the conidial 

 threads, and conidia with .an apical papilla, which germi- 

 nate by producing zoospores instead of a tube. In P. 

 Cubcnsis we have the anomaly of conidial threads which 

 follow the type of branching usually seen in the species 

 with branched haustoria, and conidia of a violet tint, such 

 as are almost unknown except among the latter group ; 

 while the haustoria are small, and the conidia have the 

 apical papilla, and produce zoospores on germination. 

 This species goes far to break down .the distinctions held 

 by some writers to exist between the two groups which 

 constitute the genera Plasmofiara and Pcronospora of 

 recent writers, though all formerly included in Pcrouos- 

 ■pora. If the distinction is to be maintained on the basis 

 of the germination of the conidia, we must then call these 

 two fungi Plasmopara australis (Speg.) and Plasmopara 

 Cubensis (B. & C). The formation of resting spores has 

 not been observed in either species, yet it is evident that 

 they have some means of surviving the winter. This is 

 equally true of a considerable number of mildews ; and 

 the problem of what substitutes for resting spores certain 

 species possess is one of the most interesting and impor- 

 tant ones connected with these fungi. 



This Department wishes to investigate all diseases affect- 

 ing cucumbers, squashes and melons, cultivated either in 

 the open air or under glass, and to this end urgently re- 

 quests all persons who suffer from any disease of these 

 crops to send specimens, with details as full as possible, to 

 the writer, as soon as it appears. 



