334 BOTANICAL GAZETTE. 



might suppose that the greater part of the species were derived from some com- 

 mon ancestor, yet, as species of fungi go, they are now comparatively distinct. 

 The same can not he said of the group Effusce. I have already noticed several 

 forms which it seems to some botanists can not be morphologically distinguished 

 from P. effusn, and, in general, all of (he Effiusa arc closely related to one an- 

 other. .Some mycologists maintain that two forms morphologically alike must, 

 if they grow on hosts belonging to natural orders which are not closely related, 

 be regarded as distinct species. I am unwilling to adopt this view so long as 

 repeated attempts have not shown that it is impossible to transfer a Peronospora 

 on one host to a host of an order not nearly related. Cultures are to lie recom- 

 mended to persons who have a certain amount of leisure, and they do not re- 

 quire an elaborate equipment or special library. One might, for instance, 

 attempt to transfer the form on Plantago to Chenopodium, or vice versa. 



In my enumeration it will be noticed that no mention is made of species 

 on Oaryophyllacece, although several are found in Europe. I believe that species 

 of Stelhria and Cerastium are attacked by Peronosporea. in the Western States, 

 but a careful search in Massachusetts has failed to detect any Peronospora on 

 such hosts, although Isariopsis pusilla Fres., which externally resembles a Perono- 

 spora, is common. It is hardly probable that we do not have some of the Calo- 

 thecce which inhabit Oaryophyllacece. P. Schleideniana Ung., on onions, and P. 

 Schachtii Fuckel, on beets, have not yet been observed in the United States as- 

 far as known, but they may be exjjected. 1 



CYSTOPUS Lev. 



( 'onidia white, spherical or cylindrical, in moniliform chains densely packed side by 

 side, forming spots surrounded by the ruptured epidermis, (termination by zoospores? 



32. C. candjdus (P.) Lev. 



Uredo Candida Persoon Syn. Fung. 233; Schweinitz Fung. Am. Bor. no. 2852 in 



part. 

 C. candidus L6v. Ann. Sci. Nat. Ser. 3, VIII ; De Barv 1. e. 126 PI. I. & II. f. 1-3 ; 



Bull. Buss. Inst, I., 429; 2<Uh Rent. N. Y. Bot. 76; Cat. Pae. Fung. 26: Bulk 



111. Mus. I., 57. PL I. f. 1-4. 

 Exs. Ellis N. A. F. no. 204 ; Ravenel Fung. Car. IV. %. 



Conidia all alike, globose, white. Oospores nearly spherical, 

 yellowish brown. Exospore marked with few, very prominent, 

 Hexuoas ridges which sometimes branch. 



On Capsella bursa-pastoris, Lepidium Virginieum, Dentaria diphylla, Sinapis 



'While attending the session of the American Association at Minneapolis 

 hist August I found the leaves of Ampelopsis quinquefolia growing on the shores 

 of Lake Minnetonka, attacked by 1'. dticola. The spots formed were small and 

 scattered, and the fungus not so well developed as when growing on grapes. 

 Strange to say the plants of Vitis riparia growing close to the Ampelopsis were 

 free from the Penmospora, and during all my excursions near Minneapolis I 

 found no Peronospora on wild grapes. This indicates that the fungus is less com- 

 mon in the Northwest than in the East, where the fungus abounds on all grapes. 

 On the other hand P. viticola has not been found on Ampelopsis in the East. That 

 it ever occurs on Ampelopsis is of importance in studying the means of prevent- 

 ing the spread of the grape-mildew. 



In September, 1883, a Peronospora was found on Geum rivale by Mr. Seymour 

 and myself at Wellesley and Newton, Mass. The conidiophores were like those 

 found on Geum album at Wood's Hall, and were sparsely scattered over the 

 leaves. Unfortunately no oospores were found, but in other respects the species 

 agrees sufficiently well with P. Potentillce. I found, in 1882, a small Peronospora 

 on Ribes Oynosbati at Wood's Hall, Mass., but the material was too poor to war- 

 rant a description. 



2 The terminal conidia are said, by Tulasne, in some cases to produce tubes. 



