KFFKCT OF r-ARAsllH I-TN(iI <>.\ THKIK IJnST. 17 



perceptible disturbing effect on the host. Such is tin- a 

 particularly with leaf-spot diseases; the tissues of isolated .-j.i.t- 

 are killed and fall out, the leaf appearing as if perforated by 

 shot, but otherwise exhibiting no discoloration or other symptom 

 of disease. In contrast to these there are fungi which, directly 

 or indirectly, bring about death of their host or SOUK- part of it. 



The simplest example of parasitic fungi killing their h"-t 

 directly is presented by one-celled or few-celled plants, which 

 soon succumb to attack even on a single cell. Where, huwevei. 

 the host is a highly orga nixed plant, its organs will resist the 

 attack of the parasite for some time. Thus with /Y////<y//////n/v/ 

 fcigi, the mycelium spreads rapidly through the tissues of ;i 

 seedling, so that death ensues in a few days. Similarly species 

 of Pen>/ii'*j)um rapidly kill leaves, branches, and fruits; likewise 

 Cfladosporium, F'i>tr/<i j>i-xtti<-n, and others. 



Somewliat different in their action are those fungi which 

 kill some tender part of a plant directly, and thereby in- 

 directly further the death of other parts dependent 

 As examples, take Pixtnl<>:-.i<i Hn/-fi;/il (Fig. 301) and 

 abietina (Fig. -03), which kill only some small portion of a 

 young plant or branch, but thereby cause drying-up of hi-h.-i 

 or distal parts. 'V //,//, /v vaccinii on stems of cowberry (Fig. 95) 

 is another example. Similarly cankers arising from X-h-i<i 

 ditissima (Fig. 80), or Peziza. Willkommii. Again, -.-///". 

 mi-Hi a* and Trtiiinti-* rodiciperda kill roots or lower portion.- of 

 the stem, and brim; about tin- death of trees of all ages. 



The case varies somewhat with certain wound-parasites like 

 Nectria '/////"//////" and ('//rti/'I>it"/-/" //'//'////. There the my- 

 celium extends so vigorously in the water-conducting or-an>. 

 as to kill thfin and h'll up the vessels, causing theivb\ 

 serious a disturbance in conduction, that branche- or whole 

 plants wither away in summer. The wood-de.stroyin- /'c/_//y /,/-,, 

 and Agaricini act similarly, altbou-b more >lo\\ly ; they attack 

 lai-'je b ranches and steins, dc-trovin- all part> of tbe wood, 

 dui'anicn us wdl as >ap-wood, and linally the bark. 



There ;ire al.-o CBSefi whi'l'e oi-jan- of the attacked hu>| 

 reniaiii alive, but suffer mi account of the hypert ropliy ,,| ,.thi-r 

 parts. In this \\;iy ].ortioii> ,,f a plant may be killed althou-b 

 not diiv.-tly the >e;it i,f tlie paia-itr. This is particularly th-- 



e where h\ pcrtrophied organs undergo increased 'ji\\th and 



B 



