522 XEAV JERSEY AGEICULTURAL COLLEGE 



Their Distrihution. — The powdery mildews are all parasitic, and 

 their abiindanee in any locality depends largely upon the character 

 of the flora. Certain groups of plants seem to be entirely exempt 

 from their attacks, and where these abound the mildews naturally 

 are less numerous than where the susceptible plants prevail. Thus 

 no mildews are met with upon the ferns and their allies. Xone prey 

 upon the pines and related cone-bearing plants. In like manner the 

 long-leaved plants, like rushes, sedges, liUies and orchids are exempt, 

 excepting the single family of grasses, and here but one species of 

 mildew is found. Therefore, the pine forests and the bogs, wlv^re 

 mosses, ferns and grass-like plants make up the vegetation, are practi- 

 cally free from mildews. But in localities where the plants are of the 

 sorts other than those just mentioned, the mildews may be expected. 

 According to Professor Salmon.* in his recent exhaustive study of 

 the group, "the headquarters of the mildews are in the Xorth Temjjer- 

 ate zone, as they occur in the greatest num]:)ers in the United States 

 and parts of Europe." It should be borne in mind that it is only 

 within a short time that milde^^•s have been carefully studied, and 

 in the vicinity of old botanical centers they are better known than 

 elsewhere. In other words, the mildew flora of Europe is much better 

 known than of Africa or Asia. With us the subject has been more 

 advanced in Xew England than the Dakotas or Texas. In =:hort, 

 there are areas in the United States where the mildew hunter has 

 not been, and therefore it is too soon to dwell at length upon the dis- 

 tribution of these fungi in our country from the economic stand- 

 point. 



Some species have been found upon but a single host. Thus, for 

 example, the Podosphtera hluncinata C. & P. is a strictly American 

 species, described in 18T2, and met with only upon the leaves of the 

 witch hazel (Hamamelis Virginiana). A glance at the herbarium 

 shows specimens from the following States : Yermont, ^Massachusetts, 

 Xew York, Indiana, Illinois, Wisconsin, Xorth Carolina, Alabama. 

 It goes without saying that the range of this mildew depends upon 

 the distribution of a single species, unless future search should de- 

 termine some other host for it. Illustrating the same point, and of 

 more economic importance, is one of the mildews of the apple. 

 Podospluera leucotriclia (E. & E. ) Sal., which is confined to our com- 

 mon apple (Pyriis mains) and another species (Pi/nis Sicholdi) and 



*A Monograph of the Erysiphacea, by E. S. Salmon. Memoirs Torrey Botanical 

 Club, New York, 1900. 



