DEVELOPMENT OF PLANTS 197 



acter of the plant as to render it impossible to state whence many 

 of the groups have been derived or what relationship they sus- 

 tain to one another. It may be stated, however, that the lower 

 fungi show unmistakable evidence of relationship with certain 

 of the green algae and that they have become degenerated owing 

 to their parasitic habit and consequent loss of chlorophyll. The 

 fungi may be divided into three classes : A, Phycomycetes or 

 Alga-like Fungi ; B, Ascomycetes or Sac Fungi ; C, Basidiomy- 

 cetes or Basidia-bearing Fungi. 



Class A. Phycomycetes 



77. Alga-like Fungi. — Some of these plants show such a strik- 

 ing resemblance to certain algae, both in the structure of the 

 plant body and in their reproductive processes, that they are called 

 the Phycomycetes from phycos, alga, and myces, mould. Atten- 

 tion will be called to three orders of this group. 



78. Order a. Saprolegniales or Water Moulds. — These fungi 

 are aquatic, living upon dead animals and plants, and as parasites 

 they are very destructive to fish. Common examples of this 

 order are seen in the whitish masses that form around decaying 

 insects in the water and in fluffy or mould-like outgrowths that 

 often appear upon the bodies of fish in aquaria. The plant body 

 consists of branching tubular threads without partitions but con- 

 taining numerous nuclei and thus resembling Vaucheria save for 

 the absence of chloroplasts (Fig. 130). The sporangia are also 

 formed by the cutting off of the tip of one of the branches by a 

 transverse wall. The contents of a sporangium, however, gen- 

 erally breaks up into a very large number of biciliate zoospores 

 (Fig. 130, C). In the species that cause so much damage to 

 fish, the spores come to rest upon the fish and form tubular out- 

 growths that readily penetrate the tissues of the fish, especially 

 where a scale has been rubbed off. Some of the hyphae also 

 extend outward from the body, causing the mould-like blotches 

 on the infected fish, and from the tips of these branches the spor- 

 angia mentioned above are formed. Most of the species of 

 Saprolegnia also form sexual organs as in Vaucheria, from one 



