CHAPTER IV 



CLASS I. PHYCOMYCETES 

 {The Alga-Uke Fungi. ^ 



The Phycomvcetes or algal fungi are characterized as follows : 



1. The plant body ranges from an undifferentiated mass of 

 protoplasm living parasitically inside a single cell to well de- 

 veloped hyphae with horizontal and vertical branches as seen in 

 the common black mould of bread. 



2. The method of reproduction is commonly asexual either by 

 the formation of sporangia or conidia. In some of the lower 

 forms these are the only methods. In the higher forms, sexual 

 reproduction by conjugation or by the normal process of fertiliza- 

 tion b}' antherids is occasional!}" or in some species commonly 

 found. 



3. In habit some are saprophytic, like many of the common 

 moulds,"^ others are parasitic. A number of well-known diseases 

 of cultivated plants are produced by members of this class of 

 fungi, notably the downy mildew of the grape, the potato rot, and 

 some of the diverse phenomena known as damping off. The fish 

 mould or salmon disease, often very destructive to young fish in 

 hatcheries also belongs to this group of fungi. 



The class Phycomycetes contains fi\ e well-marked orders ar- 

 ranged in three sub-classes distinguished by their method of sexual 

 reproduction. 



1. Archimycetes. Sexual reproduction rarely developed; my- 



celium wanting or poorly developed. 



1. Chytridiales. (Mostly parasitic on algae.) 



2. Zygomvcete-S. Sexual reproduction by conjugation. 



2. Mucorales. (Saprophytic moulds, or parasites on 

 other moulds.) 



3. Entomophthorales. (Insect parasites.) 



* A considerable number of moulds that are more or less common belong 

 to the Moniliales ; the common green mould belongs to the Aspergillales. 



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