44 A Monograph of the Erysiphaceae 



cologists on account of the peculiarity it possesses of very rarely 

 forming perithecial fruit ; in its conidial stage it is probably fre- 

 quently recorded as P, oxyacanthae. It will probably be found to 

 occur in Britain, although I have not at present seen an example. 

 It is very probable that what has been known as Oidiiun farinosum 

 Cooke will prove to be the conidial stage of the present species. 

 This Oiduun is not uncommon on apples in some parts of England, 

 and attacks especially the young leaves and leaf-buds, causing the 

 leaves to fall prematurely and hindering or completely stopping 



the formation of young wood. 



A good account and figure of P. Icucotridia has been recently 



given by Grout (154) in the Bull. Torr. Club. 



SPHAEROTHECA Lev. Ann. Sci. Nat. IIL 15: 138. 1851 



* 



Perithecia subglobose, ascus solitary, 8-spored. Appendages 

 floccose, brown or colorless, spreading horizontally and often in- 



* Kuntze (207) has recently stated that the name Sphaerotheca for the present genus 

 must give way to the earlier name Albigo, Kuntze remarks : ^/^/]^t? Steud. *' Ehrh." 

 Nomencl. (1824) Crypt. 52 and ^\-^z Sphaerotheca Lev. 1851. Y.%\s\. Albigo hiimull 

 Stea 1. '' Ehrh.*' z±zAllngo macidaris Streinz. Norn. 270. **Ehrh. in sched/'^^ Aiphi- 

 tomorpha macularis htimuli Wallr. * * * Albigo if5t zvvar ein nomen seminudum, 

 scheint mir aber sicher recognoscirbar." Kuntze then proceeds to transfer to A ibigo 

 all the species of Sphaerotheca mentioned in Saccardo's Sylloge. Magnus (232) has 

 criticised the above statements and expressed the opinion that the name Albigo has no 

 claim to be adopted, but has suggested that perhaps the name Sphaerotheca macularis 

 (Ehrh.) ought to be employed in the place of S. hnmuli DC. 



Neither Kuntze nor Magnus, however, reached the origin of the name Albigo. 

 This is found in Ehrhart's Beitr. zur Naturkunde, 7: 84. 1792, where the following 

 description is given : *' Mehlthau {^Albigo mihi zum Unterschied von der Rubigine 

 (Rost, Rotheln, Karfaugel) ^ * * ist ein weisslichtes, staubartiges Wesen, welches 

 gewohnlich auf der untern Seite der Blatter des Hopfens, der Erbsen, und mehreres 

 Pfianzen, sitzet, und zur Zeit der Reife hin und wieder mit kleinen, schvvarzen Kugel- 

 chen bestreuet ist.** Ehrhart concludes by saying that this substance is really a fun- 

 gus — '* und zvvar der Mticor Erysiphe\AViX\. ist. Wer ihn aus dieser Beschreibung 

 nicht kennen lernen kann, der schlage meine Plantas cryptogamas, n, loo, nacb, 

 wo er getrocknete Exemplare davon finden wird." M. P. Sydow kindly consulted 

 * for me the copy of Ehrhart' s Exsiccati in the Berlin Museum, and informs me that the 

 specimen No. 100 is labelled merely Afucor Eryviphe Linn. No mention of Albigo 

 occurs, nor is any diagnosis given. As Ehrhart's remarks quoted above show, this 

 author used the word Albigo in a quite general sense for all mildews, and we find it 

 nowhere defined as a genus. Consequently, there are no grounds for substituting this 

 name for Leveille's Sphaerotheca. The name *' S, macularis (Ehrh.) " which Magnus 

 has supposed should possibly supercede that of hnmuli DC. for the Hop Mildew, has 

 also no claim to be recognized. 



