68 I'REVENTIVE AND COMBATIVK MEASURES. 



plants was smaller than usual. The immunity from smut with 

 old manure is probably e.xplicable on the assumption that in 

 it the kind of nutriment suitable for the smut-conidia is ex- 

 hausted, so that any spores, which may sprout, die off. 



It must, however, be here observed that the spores of some 

 species of smut-fungi {cjj. Tilletia, the stinking brand of wheat) 

 do not germinate directly in manure, but do so in water easily. 

 The spores of most smuts are adapted to a long winter rest. 



(2) Other diseases are fought and prevented from spreading 

 by the direct extermination of the fungus or its reproductive 

 organs while in full activity on the growing host-plant. For 

 this purpose Fungicides are used, either as powders or solutions 

 applied to diseased plants. These reagents are employed with 

 most success against epiphytic fungi, where the mycelium is 

 fully exposed on the surface of the host. 



The Erysipheae are generally treated in this manner, especially 

 the powdery mildew of the vine {Oidium Tuckeri or Uncinulc 

 sjnralis). This vine-parasite is combated by dusting from time 

 to time with dry pow^lered sulphur or flowers of sulphur. The 

 sulphur may be simply shaken from a tin with perforated lid, 

 or it may be blown on by a sprayer provided with a bellows, 

 or dusted on by a sulphur-lirush, consisting of a hollow handle 

 filled with sulphur which distributes the powder through fine 

 perforations in its end to a tassel of fine bristles. In a similar 

 manner may be treated the powdery mildews of hop, rose, 

 peach, apricot, apples, etc., caused by Erysipheae. 



Fungicides are also used against fungi with endophytic 

 mycelia. The Peronosporeae cause injury to quite a large 

 number of cultivated plants, and many methods of treatment 

 have been employed against them. The mycelium lives inside 

 the host-plant, especially in its leaves, and only the conidiophores 

 make their appearance externally. Dusting with sulphur or 

 spraying with preparations of copper has on this account little 

 effect on the mycelium, but will kill the conidiophores, while 

 any conidia or oospores, which may alight on the leaves, will 

 be prevented from germinating. The most general forms of 

 fungicides are various preparations of copper, of which the 

 following are some of the more important : ^ 



' Considei-aljle liljerty has been taken here with the original. The authoi'.s 

 account has been extended with the assistance of the Journal of Mycology and 



