50 PROTISTS AND DISEASE 



Haustoria, Fig. 12, b, c, are processes growing from a 

 parasite into or among the cells of a host. They may be 

 simple and knob-like, or branched. De Bary mentions that 

 the type of haustoria just referred to in Piptocephalis is 

 exceptional. The haustoria by means of which the chytri- 

 dian Polyphagus sucks the juices of its prey must approach 

 those of Piptocephalis very closely. 



Another parasitic Mucor, Chaetodadium, is said (de 

 Bary) to make direct communications between its own and 

 its host's protoplasm at apertures where hyphae of host and 

 parasite are in contact. 



Symbiosis. Akin to parasitism is the relation of fungi 

 to algae in the symbiosis seen in lichens, of which about 

 2000 British species are known. 



In lichens the fungus alone retains the property of sexual 

 reproduction, the alga being restricted to vegetative growth 

 by the control of the other symbiont, but when gonidia of 

 lichens have been isolated and cultivated they have produced 

 sexual generations. 



The hypha of the germinating fungus- spore grows around 

 its proper alga or algae and the joint vegetation is a lichen- 

 thallus, Fig. 12, d, e. 



Nowhere is the power of protistic life more prominently 

 shown than by lichens. Towards the arctic Cladonia 

 rangiferina (reindeer moss) grows luxuriantly making life 

 possible for beast and man ; and in sub-tropic deserts 

 Lecanora esculenta grows loosely attached to limestone 



