48 Natural History Bulletin. 



phore may be recognized by the swellings at intervals upon 

 the upper part. These are rather abrupt below, but above 

 gradually taper to the next swelling. The conidia are really 

 terminal but as each conidium is formed the conidiophore 

 swells out and grows past the spore which it pushes to one 

 side. 



Peronospora: conidia elHptical, borne singly at the extremi- 

 ties of pinnately or dichotomously branching conidiophores, 

 issuing from the stomata. In some cases the branching is 

 reduced to a minimum, the conidiophore being very short, 

 with mere points for branches. 



Cystopus: the conidia which are produced in chains, collect 

 under the surface and break through by rupturing the epider- 

 mis, instead of passing through the stomata. 



In the list given below I have followed Dr. Farlow's "Enum- 

 eration of the Peronosporea; of the United States" as nearly 

 as possible. 



I owe many thanks to Mr. E. W. D. Holway, of Decorah 

 Prof. T. H. McBride, of Io\va City, and Prof. B. D. Halsted' 

 of Ames. 



The specimens from Decorah were contributed by Mr. 

 Holway, the others were collected by myself unless othei- 

 wise mentioned. 



1. Phytophthora infestans. — DeBy. 



On Solantun tuberosum. Decorah. The " potato rot." 

 Destructive in wet seasons. 



2. Peronospora alisnearum. — DcBy. 



On Cerastium nutans. Decorah. 



3. P. ALT A. — Fkl. 



On Plantago major. Ames, Iowa City (McBride), 

 Decorah. 



4. P. Arthuri. — Farl. 



On (Enothera biennis. Ames, Decorah. 



5. P. Australis. — Speg: 



On Echinocystis lobata. Decorah, Shenandoah. 



