CHAPTER X 



PHYCOMYCETES 



The Phycomycetes are commonly called the algal-like fungi. 

 They are very diverse both with reference to the characteristics 

 of the vegetative and of the reproductive stages. The habits of 

 these forms, moreover, are so varied that a discussion of such 

 peculiarities may be postponed until the individual families are 

 described. The lower forms show very little differentiation or 

 complexity of vegetative parts, and the fungous body may indeed 

 consist of a single simple cell. In other forms the fungous body 

 possesses short branches or thread-like parts, which may be desig- 

 nated hyphce. In the higher forms there is a well-developed my- 

 celium, or system of branching hyphae. These vegetative hyphae 

 are commonly siphonaceous (nonseptate), but sometimes cross 

 walls (septa) are produced. In fact, there are families in which 

 the mycelium is constantly siphonaceous until the reproductive 

 cells are cut off, and cross walls occur only in conjunction with 

 spore development. In other cases the hyphae are siphonaceous 

 when young, becoming generally septate with age. 



The methods of reproduction are either by means of nonsexual 

 or sexual spores. The nonsexual spores are produced either within 

 differentiated portions, usually tips of branches, in which case these 

 differentiated parts are termed sporangia ; or the spores (conidia) 

 may be produced upon hyphae, in which case the latter are known 

 as conidiophores. In some genera the conidia also become spo- 

 rangia germinating by the production of motile spores, zoospores. 

 Sexual reproduction by the union of differentiated cells (gametes) 

 is common in the higher forms only, and the gametes may be 

 equal or unequal in size. The higher forms, however, constitute 

 the majority of these fungi. 



The Phycomycetes contain seven orders. Two of these, Ancy- 

 listales and Monoblepharidales, are small groups of water fungi. 

 One order, the Mucorales, is an unusually interesting group, 



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