FUNGI. INTRODUCTORY 



407 



The effect of the parasitic invasion may be the death of the host, 

 where vital parts are destroyed, as in attacks by Pythium, or Armillaria 

 mellea (Fig. 340). But in many cases the attack is tolerated by the 

 host, with only partial injury. It is often the leaf, or only certain 

 tissues of the leaf, which are attacked, the result being a loss of 

 efficiency by the host, while the parasite gains access to the sources 

 of supply. These may indeed be stimulated to greater action, with 

 the effect of swelling, and extra divisions of their cells. The result 

 may be various malformations, such as are seen in the familiar leaf-curl 

 of Peaches, or the swollen patches of Cluster-Cups (Fig. 383, p. 447). 



FIG. 342. 



Successive stages of the penetration of cell-wall of Lily by the hypha of the 

 Fungus causing the Lily disease. (After Marshall Ward.) See Text, p. 406. 



The attack may, however, be upon the stem or root, or even the 

 ovary. The effect is to produce swellings and malformations such 

 as those of the roots of Crutifers, called " Club-root " (Fig. 343), 

 or of the grain of " Ergot of Rye " (Fig. 341). 



Some Fungi lead a constantly parasitic life, as the Rusts (Uredineae) 

 do. Others are as constantly saprophytic, like the Saprolegniae. 

 Others again may be sometimes the one, sometimes the other : and 

 this may be so in the individual life. Thus Pythium, the " Damping- 

 off Fungus," attacks the seedling-host, and kills it, but continues to 

 live on the corpse (p. 413). It is first parasitic, then saprophytic. But 

 the converse has been shown in Sclerotinia sclerotiorum, where a period 

 of saprophytic nourishment is a necessary condition for its success 

 in perforating the living host. It has been regarded as a Fungus 

 which is in course of " education " for passage from the saprophytic 



