10 



THE PARASITIC FUNGI. 



others, like Podosphaera castagnei, they take the form of broadened 

 closely- clinging hyphae with haustoria. Frank describes a swell- 

 ing of the germ-tube of Fuskladium tremulae just before the 

 infecting hypha pierces the' cell- walls of its host. A similar- 

 phenomenon can be observed in Polystigma rubrum, in Gnomonia 

 erythrostoma, and in the germinating aecidiospores of Melampsora 

 Goeppertiana. Some other examples will be mentioned in our 

 next section. 



Haustoria of the epiphytic Parasites. 



The most inconspicuous haustoria are those of Herpotrichia 

 nigra and Trichosphaeria parasitica, described by R Hartig.^ 



Fio. 2. — Haustoria of Ti-ichoaphaeria parasitica. 

 (After R. Hartig.) 



(Details on Fig. 88.) 



They are tiny hyphal processes resting on the host-epidermis, 

 and sunk into the outer walls of the epidermal cells, so as to 

 pierce the cuticle but not the whole wall (Fig. 2, d, e; also 

 Fig. 90). The Erysipheae are typical epiphytes, which weave 

 a mycelium over the surface of plants they attack ; the 

 mycelium retains its hold by adhesion-discs or appressoria, and 

 from certain parts of these a fine thread-like process is given 

 off, which, after piercing the epidermal wall of the host, sweUs 

 inside to a simple or branched sac, the haustorium. The 



'^ Lehrhuch d. Baumkrankheiten, II. Aufl. English translation by Professor 

 Somerville. Macmillan & Co., 1894. 



