242 TEXT-BOOK OF FUNGI 



Leptomitus lacteus, a species not uncommon in ditches and 

 rivers, more especially where organic matter is emptied 

 from manufactories, etc., illustrates this structure. This 

 feature also has it counterpart in algae. 



In some genera belonging to Chytridieae, as Rozella 

 and Reessia, the protoplasm during the vegetative condition 

 is not enclosed by a cell-wall, but remains naked and 

 amoeboid in the cells of the host. 



Klebs, in studying Saprolegnia mix fa, came to the con- 

 clusion that gemmae are of no value from a phylogenetic 

 point of view. They are special structures, whose use is 

 to tide over periods when the formation of other spores is 

 precluded. They behave like ordinary hyphae, and give 

 origin to oogonia or sporangia depending on environment. 



The special structures that give origin to zoospores are 

 called zoosporangia. 



All the species are minute, and come under the category 

 of microscopic fungi ; some species consist of a single cell, 

 entirely destitute of mycelium. 



A considerable number are parasitic on plants or 

 animals, as Phytophthora infestans, causing the too well- 

 known potato disease, and Saprolegnia ferox, the origin of 

 the equally destructive salmon disease. 



Many species are truly aquatic, and have spores pos- 

 sessed of voluntary movement, hence called zoospores. 

 The great majority of fungi that have adapted themselves 

 to aerial conditions have ceased to produce zoospores, 

 non-motile spores, diffused by wind, insects, birds, and 

 ether agents, having taken their place. The fungus causing 

 potato disease, Phytophthora tnfestans, is an illustration of 

 a connecting link between the primitive aquatic fungi and 

 their modern aerial descendants. Although this fungus 



