DISPOSITION OK PLANTS To KlsKAM:. 61 



situations favour repn Auction of mildew and other di.-eases ; 

 under such conditions a rapid increase of potato-di-ea-e during 

 July is easily observable and may be safely foretold. 



The extension of //< /yW/-/V//"/ is greatly facilitated by snow, 

 which weighs down young plants or branches of spruce and 

 pins them to the soil, where the fungus develops on its host 

 under the snow-covering, (hi this account elevated situations 

 and hole-planting render the spruce liable to disease 



Many plants which, as a rule, sutler from fungus-diseases 

 will be found to remain exempt in open or dry situations, or 

 during a dry period. The tops of trees are not attacked by 

 many fungi which frequent the lower parts of the crown. This 

 is particularly the case with epiphytic lichens and certain fun-i. 

 which require a high degree of air-moisture. Trichosphaeria 

 jHd-iisitii-rt, always very abundant in damp silver tir regenerations, 

 is almost absent from free-standing trees, or from the higher 

 parts of the crown in closed forest. It is, in fact, a parasite 



well adapted for extension in the crowded ma natural to 



the early growth of the fir, and the host is, during its youth, 

 disposed to disease from this particular parasite. A fungus on 

 the beech behaves similarly, occurring in Havana only in the 

 very dam}) parts of close high forest and in Alpine gorges. 

 Other fungi have Letter means of protection against drought, 

 for example, ////x/> //'///// macrosporium has its spores enclosed in 

 gelatinous envelopes and may be found on the highest point of 

 the spruce', although, on the whole, its distribution is nm-t 

 favoiiieil by moisture. Fungi which frequent algae, or are di-- 

 tributed by means of x.oospores, depend absolutely on moisture: 

 hence they frequent ho--- Liouin- mi banks of .streams, pl.-n -e- 

 liable to flooding, or low-lving moist meadows, whereas the -anie 

 host-species remain- completely exempt from their atlaek- j n ; , 

 dry locality. 



A plant mav be said to be in a condition of abnormal 

 disposition to disease \\hen depri\ed of its natural protection. 

 Thus wound* of any kind render a plant di-po-ed to infection 

 from wound-para-ite-. which are unable to harm uninjured part-. 

 After severe hail-^toims an outbreak of Nectria iliti.^i in" is not 



linfrei|llellt alllon'J-t 1 e<jeliel ated beech, or e\ell ill tile e; p\ 



of older forest. I ha\e ;d-n observed an e\ten-i\ (break of 



i-in lulu/mi on lal m i mi in Hear Munieli. obvioii>l\' 



