Chapter 5 

 THE PHYCOMYCETES 



Phvcomvcetes fascinate the observer mainly for the reason that 

 so many of them can be induced to carry on all their activities 

 fully exposed to microscopic view. As their name indicates, the 

 Phycomycetes are algal fungi. They might better be regarded 

 as the sporangial series of fungi and hence designated Sporangio- 

 mycetes. Early students of this group and even some modern 

 workers regard the Phycomycetes as degenerate algae. Those 

 who hold this belief assume that by loss of chlorophyll and con- 

 sequent loss of ability to elaborate food, algae may have become 

 fungi. The merits of this assumption need not be discussed at 

 this point, but it may be pointed out that this behef emphasizes 

 morphological resemblances between algae and fungi and ignores 

 almost completely physiological differences. 



The Phycomycetes include approximately 300 genera and more 

 than 1500 species. They constitute a very diversified assemblage, 

 ranging from species whose entire thallus consists of a micro- 

 scopic spherical cell to those with a conspicuous, filamentous, 

 branched thallus. Some are strictly parasitic, living on algae, 

 ferns, seed plants, and other fungi, and at the opposite extreme 

 some are wholly saprophytic. Some are aquatic, some amphibi- 

 ous, some terrestrial. 



The thallus. The assimilatory portions of this group as a 

 whole are coenocytic; that is, they are non-septate and multi- 

 nucleate. Septations commonly are formed, however, in con- 

 nection with the development of reproductive structures. They 

 may also appear in old hyphae, such as those in Mucor, Sapro- 

 legnia, and Phytophthora, the segments becoming chlamydo- 

 spores or gemmae. Septations regularly appear in young thalli 

 of certain other genera, for example, Basidiobolus, Allomyces, 



and Entomophthora. 



57 



