26 A Monograph of the Erysiphaceae 



cati is appended. Only those are quoted which have been per- 

 sonally examined, and unless prefixed by an asterisk, or followed 

 by information as to the source, all the numbers refer to the copies 

 in the Kew Herbarium. Those distinguished by an asterisk are 

 to be found in the Herbarium of the British Museum (Natural 

 History). It is necessary to state exactly what copies have been 

 examined, as — In the case of microscopic fungi especially — different 

 copies of the same numbers in exsiccati may contain different species. 

 I have not attempted to deal with the described species of 

 Oidium in the present w^ork, only . mentioning those which are 

 generally admitted to be the conidial stage of known species of 

 the Erysiphaceae, as, e. g,, 0, Tnckeri and Uncinnla necat&i% O. 

 monilioides and ErysipJie graminis^ etc. In all probability the 

 genus Oiduim is not autonomous, 'but consists entirely of conidial 

 forms of the Erysiphaceae. About 50 species of Oidiiivi have been 

 published ; of these six are already known to be the conidial stage 

 of certain species, and over twenty- five of the remaining species 

 grow on plants known to be the hosts of species of the Erysiphaceae. 

 I have not included in the descriptions of the species of W\^Erysi- 



F 



phaceae the characters shown in the conidial iOidiiiui) stage. In 

 many species, indeed, this stage has not, at present, been observed. 

 In those cases where only dried material was available, the ex- 

 amination would not have been satisfactory, as in studying the 

 Oidiiim^orva living material is necessary in order to arrive at such 

 characters as the number of conidia produced in the chain, the 

 size and shape of the ripe conidium. I hope at some future time 

 to investigate this branch of the subject. 



The material examined has been for a large part found in the rich collection of 

 Erysiphaceae in the Royal Herbarium, Kew. This collection includes the types of 

 Cooke and Feck's American specieS; and is especially valuable in containing Berkeley's 

 herbarium. In this occur, besides Berkeley's types, no less than 98 specimens sent by 

 L6veille to this author (Leveille's herbarium, M. P. Ilariot informs me, was destroyed 

 in 1870 during the Franco-Prussian war); also a number of specimens sent byCastagne, 

 Roberge, etc., and a few examples from Schweinitz' herbarium. For the great facil- 

 ities afforded me in the use of this collection I am under obligations to the Director of 

 the Royal Gardens, Kew, 



Next in importance has been the private collection kindly sent on loan by Prof. 

 F. S. Earle. This contains over 800 excellent specimens of the American Erysiphaceae^ 

 and is valuable as being the material used by Professor Burrill and Professor Earle in 

 their well-known work on the family (61). 



