42 A Monograph of the Erysiphaceae 



dactyla^ to which plant I consider P. leiicotricha to be most nearly 

 allied. From all known species of Erysipheae the present plant 

 differs in possessing two kinds of appendages, and suggests, I think, 

 the manner in which Sphaerotheca may have arisen from some 

 such genus as Podosphaera. In the present species there are signs 



w 



that the more specialized apical appendages are beginning to die 

 out, as is shown by the fact that these only rarely dev^elop to the 

 stage of forking, commonly remaining undivided and blunt at the 

 apex. On the other hand, the Sphaerothcca-\\Vic basal appendages 

 have already appeared. These are sometimes obsolete, sometimes 

 well developed and densely clustered. 



P, leiicotricha was known only from North America, until 

 Magnus (228) recently reported it from the Tyrol. It appears 

 certain, however, that it is really quite common in parts of Europe 

 in the Oidium stage on the young stems and buds of apple, but 

 that it has been passed over on account of the fact that it only very 

 rarely produces perithecia. Professor Magnus kindly sent me his 

 specimens from the Tyrol for examination, and I found them to 

 agree perfectly with American examples. 



Quite similar to the Tyrolese specimens are Russian ones 

 which I have found contained in the Herbarium of St. Petersburg, 

 under the name of Sphaerotheca castagnei (W. Wahrlich, Parasit, 

 Pilze, 17 and 18); this is also the case with the specimens (simi- 

 larly named) from Germany issued in Syd. Myc. March, no. 3 161. 



P, leiicotricha has also occurred among the Japanese Erysiph- 

 aceae sent to me by Prof Miyabe. This example (now in the 

 Kew Herbarium) is growing on Pynis Toringo {P, Sieboldi), and is 

 without doubt the same as the American and European species. 

 The apical appendages are here sometimes very poorly developed, 

 or even apparently absent, sometimes long and characteristic ; the 

 curious root-like basal appendages are developed prominently. 

 The perithecia are clustered in the characteristic manner, forming 

 blackish masses on the persistent white powdery mycelium. This 

 occurrence, besides adding Asia to the range of distribution, gives 

 a new host-plant for the species. 



P.- leiicotricha is so prev^alent in some parts as to form a disease. 

 Pammel (267) says " In some parts of the United States apple 

 seedlings are seriously affected with this disease. It rarely affects 



