DEVELOPMENT OF PLANTS 



207 



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, generally 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 outgrowths 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 



^tVim 



Fig. 130. Features in the life history of the water moulds: A, fly in- 

 fected with Saprolegnia, showing the tubular threads of the fungus radi- 

 ating out from its body. B, tip of a tube magnified, showing an early stage 

 in the formation of the sporangium. C, sporangium discharging zoospores. 

 D, Reproductive organs of a related fungus, Achlya — 0, oogonium contain- 

 ing four female gametes; an, antheridium with tubes penetrating oogonium 

 for transport of male gametes. 



fish, and from the tips of these branches the sporangia mentioned 

 above are formed. Most of the species of Saprolegnia also form 

 sexual organs as in Vaucheria, from one to several gametes being 

 formed in an oogonium (Fig. 130, D). The antheridia, however, 

 develop several non-motile male gametes. This peculiarity of 



