34 TEXT-BOOK OF FUNGI 



by a vesicular membrane which separates it from the 

 protoplasm in the cell of the host. The haustorium is the 

 absorbing organ which supplies the fungus with food, at 

 the expense of the cell of the host in which it is located. 

 The nucleus of the host-cell is usually not interfered with. 

 In the majority of the Erysipheae the haustoria are of 

 the type described above ; in some instances, however, the 

 haustoria show indications of a type of structure met with 

 in other groups. In Erysiphe graminis the haustoria 

 branch into a number of finger-like outgrowths. In 

 Phyllactinia, another genus belonging to the Erysipheae, 

 branches of the superficial hyphae enter the leaf through 

 stomata, wander for a short distance in the intercellular 

 spaces of the leaf, and send off haustoria into the cells. 

 Sappin-Trouffy has shown that in the l)redineae, haustoria 

 are as well developed as in the Ustilagineae and the 

 Peronosporeae, the nucleus of the host-cell being attacked 

 and deformed. 



In the Peronosporeae intercellular mycelium is abun- 

 dant in the tissues attacked ; usually leaves, and haustoria 

 penetrate the cells by a narrow neck, which forms inside 

 the cell several more or less elongated, multinucleate 

 branches. In the mycorrhiza of orchids and other plants, 

 the haustoria usually grow directly towards the nucleus on 

 entering a cell, and envelop it in a dense hyphal coil. 



In some instances the fungus is fixed to the substratum 

 by means of many independent fascicles of hyphae which 

 are spoken of as rhizoids ; this arrangement is very evident 

 in the genus Rhizina^ also in Lichens, as the species of 

 Peltigera. Such rhizoids perform the dual function of 

 organs of nutrition and of mechanically fixing the plant 

 to its nutrient body. 



