PYTHIALES. 



99 



taining themselves for long periods as saprophytes. Some of 

 the Pvthiales attack other fungi, algae, and insects or are said to 

 be the mvcorrhizal component in liverworts and ferns. Zo- 

 ophagus is predaceous. Alany species live in the soil. 



Fig. 29. Structures possessed by Phytophthora. A. The mycelium in 

 culture is irregular in diameter and may have many nodular bodies. B. 

 Sporangiophores that branch below the last-formed sporangium. C. Spo- 

 rangium M-hose content is cleaved preparatory to opening at the papilla to 

 permit the zoospores to escape singly. D. Sporangium that is partly 

 empt)- with a swarm spore in the orifice. E. After coming to rest, the 

 swarm spore germinates bv germ-tube formation. F. .Multinucleate anthe- 

 ridium and oogonium that arise as termini of lateral branches. G. All 

 nuclei except one in each organ disintegrate, and a fertilization tube forms 

 for passage of the antheridial nucleus into the oogonium. H. Paragynous 

 antheridium. /. Androgynous antheridium. 



The Pvthiales, by and large, are essentially aquatic, as their 

 biflagellae zoospores, produced in sporangia, indicate. In some 

 instances, however, the sporangia germinate directly by the for- 

 mation of a ^erm tube. Normally the zoospores encyst after a 

 period of swarming, and further development is initiated by the 

 formation of a hvpha. 



