MODE OF LIFE OF THE PARASITIC FUNGI. 11 



haustoria of Podosphaera castagnei (Fig. 71) are bladder-like, 

 those of Oidium Tuckeri are lobed. 



. The simplest formation of haustoria consists in an outgrowth 

 of the mycelium which depresses the cell-wall of the host 

 without piercing it (e.g. Peronospora densa). In other cases the 

 cell-wall, at first only depressed, becomes ultimately broken 

 through. 



Certain lower fungi live parasitic on other fungi and adhere 

 to their hyphae by means of well-developed adhesion-discs from 

 which haustorial structures are formed inside the hyphae of the 

 host. Thus Piptocephalis fresenia is parasitic on hyphae of some 

 species of Miicor, and produces from a swollen bulb-like appres- 

 sorium a tuft of very fine haustoria inside the J/wcor-hypha. 

 Syncephalis proceeds even further, for the haustorial process grows 

 and branches inside the host, becoming, in fact, an endophytic 

 mycelium. A further advance towards endophytic parasitism 

 is presented by the Chytridiaceae, low forms of fungi living 

 on algae or fungi ; some send haustorial structures into their 

 host, others develop a mycelium whose attack however is 

 directed against only one host-cell. Fischer, in his "Phycomy- 

 cetes," thus describes the latter forms : " The vegetative body, 

 a resting swarmspore, consists of a spherical or ellipsoidal part 

 which becomes a sporangium, and of a filamentous vegetative 

 portion which spreads through the host-cell as a haustorium or 

 mycelium and dies away after the formation of the sporangium. 

 This primitive mycelium is unicellular, and may be unbranched 

 or very finely branched." 



2. Acquisition of nutriment by the endophjrtic parasitic 

 fiingi. The simplest case of the endophytic mode of life is 

 presented by those fungi which vegetate in the epidermal 

 membranes of their hosts, and derive their nutriment osmotically 

 through the inner cell-walls. They live covered by the cuticle, 

 which must have been penetrated by an infecting hypha at the 

 time of first attack. This mode of life is exhibited by many 

 fungi, particularly by the Exoasceae ; the mycelium of these 

 vegetates under the cuticle of the host plant, and ruptures it at 

 the time of ascus-formation. In spite of their limited distri- 

 bution the species of this group so influence the development 

 of their hosts as to induce pustule-like outgrowths, crumpliug 

 and distortion of leaves, and even "witches' brooms." In some 



