177 



OBSERVATIONS ON THE LTFE-HISTORY OF THE 

 AMERICAN GOOSEBERRY-MILDEW {SPHAERO- 

 THECA MORS-UVAE (SCHWEIN.) BERK.i 



By E. S. salmon, F.L.S., 



Reader in Mycology, University of London ; 

 Mycologist to the South Eastern Agricultural College, Wye, Kent. 



The rule among the species of the Erysiphaceae — to which the 

 American gooseberry-mildew belongs — is a life-cycle consisting of the 

 production of a conidial stage during the growing-period of the host- 

 plant, and the production before the advent of winter of a perithecial 

 stage. In the co7iidial stage the spore is a naked, short-lived conidium ; 

 in the perithecial stage the spore is an ascospore which remains living 

 for several months within the ascus inside the thick-walled perithecium. 



While this is the usual life-cycle, some striking exceptions occur, 

 particularly in cases where a species has found its way into a new 

 continent. 



When the vine-mildew {Uncinula necator (Schwein.) Burr.) invaded 

 Europe, no perithecial stage was found associated with it for the first 

 47 years^, the mildew existing during winter in the conidial stage in 

 a more or less dormant condition. Appel has shown that before winter 

 patches of hibernating mycelium are found on the stem of the vine ; 

 these produce conidia the next season. These hibernating patches have 

 thicker-walled hyphae, and more numerous and larger haustoria. 

 Although the perithecial stage of U. necator has been found within recent 

 years on a few occasions in different years in France, Germany, and 

 elsewhere, it appears that the production of ferithecia — which are 

 formed abundantly in America, the native home of this mildew — only 

 takes place excejJtionally in Europe — possibly under abnormal weather 

 conditions. 



^ Paper read at the Meeting of the Association of Economic Biologists, on April 17, 

 1914. 



2 Salmon, E. S. A Monograph of the Erysiphaceae (Mem. Torrey Bot. Club, ix, 1900). 



