332 FUNGI 



them attaining and entering l)y the apical opening of the oogone, and 



uniting with the oosphere. The resulting oosj^erm has not yet been 



observed to germinate. 



Propagation takes place by the formation of uniciliated zoospores in 



zoosporanges, from which they escape in the same way as those of 



Phytophthora. 



Literature, 



Cornu — Monogr. des Saprolegn. {Joe. cii.). 



Order 4. — Saprolegnie^e. 



The Saprolegnieoe, as their name indicates, are saprophytes on the 

 dead bodies of both plants and animals in water ; with at all events the 

 exception of the Saprolegnia of the salmon disease, which is both sapro- 

 phyte and facultative parasite. The cause of the predisposition to this 

 disease has not yet been exactly determined, as for example has been the 

 case with those species of Pythium which possess a similar mode of life. 

 Prof, de Bary points out with regard to them that susceptibility to disease 

 in the host is in relation to the amount of water present. The problem 

 in the case of the salmon disease has every appearance of being a more 

 complex one. The Saprolegniese bear in other respects much resem- 

 blance to the Peronospore^, and especially to Pythium, which until 

 recently was included among the former. Pythium indeed presents 

 points of relationship with the types of Oomycetes in general ; and the 

 relationship is rendered the more striking by the union in some of its 

 species of both parasitic and saprophytic modes of life. The thallus- 

 hyphae of the Saprolegnieas are usually of relatively large size, springing 

 from slender rhizoids buried in the substratum. 



The oogones arise, as in Peronospore^, on branches of the thallus- 

 hyph^. In most cases, however, several oospheres are formed in each 

 oogone (sometimes as many as thirty or forty), and, no periplasm having 

 been differentiated, the whole of the oogonial protoplasm is included in 

 them. It happens in some cases that only one oosphere is formed, 

 but the number is variable according to species, and also partly according 

 to individuals. Pits arise, but by no means always, in the oogonial wall. 



The antherids, which are commonly club-shaped, are produced on 

 slender branches of the thallus ; and each antherid is borne either on 

 the same hypha of the thallus as the oogone to which it is attached, or 

 on a hypha which bears no oogones. The remarkable point about 

 these antherids is their impotency, since no actual observation of the 

 transference of protoplasm from them to the oospheres has ever been 

 made, though they perforate the oogonial wall, and processes, like 

 impregnating tubes sent through, come in contact with the oospheres. 

 These processes grow from one oosphere to another, and may even 



