Historical . , 11 



In the Erysiphaccae, as in other groups of parasitic fungi, we 

 find that in some years, from unknown causes, the species attack 

 certain host plants in a marked manner. This is well illustrated 

 by the wave of disease, caused by Sphacrothcca hinnuli, which 

 periodically sweeps over the cultivated hop, and in the attacks, 

 by the same fungus, in certain years on cultivated strawberries ; 

 and it is not the less noticeable with regard to wild host-plants. 

 Some interesting biological notes, on this and other points, are 

 given by Griffiths, in his paper on *'Some Northwestern Erysipha- 



ceae" (152). 



The frequency with which great devastation is caused by mem- 

 bers of the present family to cultivated plants of high economic 

 value makes the study of their life history a matter of importance. 

 The two worst diseases are those caused by the vine and hop 

 mildews {Uncimila necator and Sphacrotheca hniinili), which at 

 certain periods have caused wholesale destruction to the cultivated 

 vines and hops of the world. Other well-known diseases are 

 caused by the rose mildew {Sphacrothcca pannosa), the apple 

 mildew {Podosphaera leiicotricha) and the pear and cherr>- mildew 

 {P. oxyacanthac), the goosebeny mildew of America {Sphacrotheca 

 vwrs-tivae) and the gooseberry mildew of Europe {Microsphacra 

 grossidariac), the pea, bean and turnip mildew {Erysiphe polygon!), 

 and the corn mildew {E. graminis). 



All these diseases, it is now proved, are able to be held in 

 check by the prompt use of certain fungicides. I have endeav- 

 ored to give full instructions for the preparation and use of the 

 best remedies under each species of mildew causing a disease. 



Historical 



Sp 



under the name of Mucor Erysiphe—'' Mucor albus, capitulis fus- 

 cis sessilibus. Habitat in foliis Huviuli, Accris, Lamii, Galcopsidis, 

 Lithosperviir By this name the four species of the Erysiphaceae 

 now known as Sphacrotheca humuli, Uncinula aceris, Erysiphe 

 galcopsidis (on Lamium and Galcopsis) and E. cichoracearum were 

 in all probability Intended. In 1767, in the " Mundus Invisibdis " 

 (222) Linnaeus spoke of Erysiphe as a genus (giving, however, no 

 strict definition). Persoon, in 1796 (Obs. Myc. 1 : 13), gave the 



