Peach Curl 



in stoves in this country. It is certain, too, that 

 conditions which keep roses growing without a 

 check render attacks of mildew less Ukely. 



A remarkable instance of the dependence of 

 fimgus attack upon external conditions, unfavour- 

 able to the host but favourable to the parasite, is 

 afforded by the leaf -curl disease of the peach, 

 practically unknown when the plants are grown 

 under glass or in sheltered situations, frequent and 

 disastrous in plants exposed to cold winds and other 

 retarding influences. Damping - off in seedlings, 

 again, one might be tempted, but for the manner 

 in which the trouble spreads, to attribute solely to 

 close seeding and close, damp conditions, yet a 

 fungus is always involved too. 



We have thus more than one cause contributing 

 to the development of the disease — ^the fungus itself, 

 the constitution of the host-plant, and the nature 

 of the environment which influences either the host 

 or the fungus or both. 



The mycelium of the parasite is usually not 

 external as it is in the mildews. It generally burrows 

 about inside its host in its search for food, creeping 

 between the cells and sending suckers into them, or 

 passing through them. It may produce a poison 

 which actuaUy kills the cells it comes in contact with 

 (even some little distance ahead of the mycelium), 

 or grow without doing more harm than arises from 

 robbing the plant of some of its sap and diverting 



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