ON THE SAPROLEGNIE^. 189 



produce new Saprolegniess, apparently just as well as if they were 

 fertilised. In contrast to the development of oospores without fer- 

 tilisation, is the occurrence of antheridia, the tubes of which do not 

 penetrate into the oogonia, but open and expel the fertilising par- 

 ticles into the surrounding water.* The fertilised oospores clothe 

 themselves with a thick, firm cell-wall, and remain dormant in the 

 oogonium for months. These are the resting-spores, which fall off, 

 sink to the bottom of the water, and rest through the winter. 

 Thus nature has provided against all the zoospores being des- 

 troyed by a hard winter and the fungus extirpated, by enclosing 

 from five to twenty in a thick, tough skin or shell, which rests 

 quietly in the water until the return of spring. 



This account of the development of the Saprolegnieae applies 

 generally to the whole group ; but there are various details to be 

 noticed, by which the different genera are recognised. The diffi- 

 culties attending the identification of the various genera are many, 

 for, as is now known, the generic characters seem to depend on 

 the mode of formation and evolution of the zoospores, and the 

 specific characters on the conditions of the sexually-developed 

 reproductive organisation, and on the special figure of the oogonia. 

 Hence, unless one be successful in finding one of these plants in 

 a sufficiently early condition to gain a view of the formation of 

 the zoospores, which ordinarily precedes the true fructification, its 

 generic position cannot be definitely predicated. On the other 

 hand, if one sees the zoospores only, and thus establishes the 

 genus, but fails to get a view of the conditions of the other type 

 of fructification, the species to which any particular plant belongs 

 must remain undetermined. 



The following are the principal genera, with their special 

 characteristics : — 



I. — Saprolegnia. In Sapj'olegnia, when the zoospores have 

 escaped from the apex of the sporangium, a new spore-case is 

 developed from the septum, and grows up within the old case. 



* These observations on the fecundation of the oospores are on the authority of 

 Comu, who in 1872 pubhshed an exhaustive monograph on the Saprolegnieae, but 

 De Bary, after more recent and prolonged researches, has come to the conclusion 

 that, although the fertilising tubes of the antheridium do m some cases enter the 

 oogonium, yet they always remain closed at the end, and never enter the substance 

 of the oospores, and that no observable passage of anything takes place through 

 the fertilising-tubes. 



