206 REPRODUCTION OF A WATER MOULD 



it will be found that the entire body is composed of a mass of 

 these delicate hyphae which spring from a mycelium in the 

 ground. We shall expect to find remarkable departures in the 

 fungi from previous types because of their peculiar manner of 

 obtaining food and also because they are largely terrestrial plants 

 and therefore exposed to a much wider series of conditions than 

 in the case of the algae. This will tend to cause variations and 

 so bring about new structures that are in harmony with the con- 

 ditions under which the plants live. As a rule, these variations 

 have been so extensive and have so completely changed the char- 

 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. 

 Attention will be called to three orders of this group. 



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

 are either saprophytes, living upon dead animals and plants, 

 or parasites. In this latter relation one form causes a destructive 

 disease in fish while another genus produces the damping off and 

 decay of seedlings. They are all microscopic plants and many 

 are aquatic. 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 branch- 

 ing tubular threads without partitions but containing numerous 



