Ch. X] 



THE ALGAL FUNGI 



435 



spores, either free-swimming or wind-carried, according to 

 habit, and in part sexually by methods almost identical with 

 those in Green AlgaB. They fall into three principal orders 

 as follows : 



Saprolegniales: the Water Molds. 

 Peronosporales: the Blights or Downy Mil- 



Order 1. 

 Order 2, 



DEWS. 



Order 3. 



Mucorales: the True Molds or Black Molds. 



Order 1. Saprolegniales (Oomycetes in part): the 

 Water Molds. These live on the floating bodies of dead 

 insects, tadpoles, and small 

 fish, where they appear as 

 a woolly wrapping of white 

 hyphae, while they also 

 attack small living fish, 

 through the gills, often 

 causing great losses in fish 

 hatcheries. In the common 

 and typical Saprolegnia 

 (Fig. 302), the plant body 

 suggests a mass of colorless 

 Vaucheria threads, com- 

 posed of multinucleate cce- 

 nocytes, sending haustoria 

 into the substratum or host. 

 Asexual reproduction oc- 

 curs through biciliate zoo- 

 spores formed in elongated 

 sporangia. In sexual re- 

 production (when present, as it often is not), lateral oogonia 

 are formed in which are usually several egg cells ; tubular 

 antheridia grow towards and into contact with these oogonia, 

 into which they send tubes carrying each a sperm nucleus to an 

 egg cell, a method curiously anticipatory of that used in the 

 fertilization of the egg cell by the sperm nucleus in the pollen 

 tube of the higher plants. The resultant oospores acquire 



Fig. 302. — Saprolegnia species. As 

 it appears ordinarily on a dead insect in 

 water, natural size, and portions, X 200. 



Left, the coenocytic hyphae bearing 

 oogonia, with fertilization of the egg cells, 

 in various stages ; and right, formation 

 of zoopores. (Chiefly from Kerner.) 



