CHAPTEB VII. 



ECONOMIC IMPOKTAM E OF DISEASES OF PLANTS. 



1 3. The economic importance of any plant-disease depend- "ii 

 its distribution, its intensity, and the value of the plants attacked. 

 < )f most consequence are those epidemic diseases of fungoid origin, 

 which cause, rapid death (if their host, and spread with threat 

 rapidity over wide areas. Such, through repeated attacks. 

 may render the cultivation of certain plants impi>iMe 

 in a locality. Almost equal damage may result from those 

 parasites, which, although they do not kill their host, yet 

 de-troy or prevent the development of that part for which we 

 urow the plant. Amongst these are species which inhahii 

 flowers or fruits, the wood-destroying fuimi of forest-trees 

 and forms inimical to the folL^e, roots, or tuliers of jilants 

 of economic value. 



A- examples of parasitic fun^i which hrini; alioiit rapid death 

 of their host, are the originators of many diseases of youiiL. 1 

 plants. riii/tn^litlini-n omnivora may during a few days of damp 

 weather completely kill out not only healthy l>eds of seedling 

 lii-eel) or conife]-> in the nursery, hut even the yoiin^ plants 

 hy which a forest is heinu naturally re-'-neratrd. l'< Jl,,;\i,i 

 ll'iff I'jii, a few years a-o in the heech-foivsts in sonic .! 

 of I'.avaria, extel'iiiinated three-fourths of the na!iirall\ --own 

 plant< from OIK- to four years old. 1 1 ,/mt ,-irli in /iii/rn is 

 capalile of coni|iletely ,\,^[ roving the yoiin- sj.nice plantal: 

 so importaiii for the alforestrai ion of hare -lope-; in mountainous 

 distriel-. and it may attack with such violence nur>erir- 



lili-heil at '^reat cost and labour that lhc\' have to he 



