February, 1898.] 29 



ON THK GENUS IvEPTOI^KGNIA OF THE 

 SAPROLEGNIACE^, 



WITH THB DESCRIPTION OF A NKW SPKCIKS, AND REMARKS 

 ON A SPECIAI, FORM OF CHI^AMYDOSPORES. 



BY AI,I,AN P. SWAN, F.Iy.S. 



[Plate ij. 



The Saprolegniaceae are microscopic plants, which lead 

 aquatic lives. They are of very general distribution ; prob- 

 ably there is no natural open water in Ireland in which they 

 are not present. The family, by the latest classification, 

 consists of eleven genera, and more than forty species, all of 

 which are of saprophytic habit. 



Their study is somewhat tedious owing to the difficulty in 

 obtaining pure cultivations, and also to the long period 

 which must necessarily elapse — say seven to twelve days^ 

 before the life-cycle of any species is sufiiciently complete to 

 allow of its certain identification. 



Their vegetative organs consist of tube-like filaments with 

 a continuous cavity. These are of two kinds ; internal threads, 

 which penetrate the nutrient substance, on which they live, 

 serving as roots, and the external filaments which spring 

 from them and grow outward into the surrounding water. 

 It is on these latter that the organs of fructification are borne, 

 and it is upon them, and the characteristic behaviour of the 

 spores which they contain, that the generic classification is 

 mainly based. When these filaments — which in a sense are 

 like the stalks of the grasses — have attained a good healthy 

 growth, they develop their organs of reproduction, which are 

 of two kinds, sexual and non-sexual. 



The non-sexual fruit is developed in an organ called a 

 zoosporangium, and the zoospores which it serves to produce 

 and distribute are the active agents for the rapid reproduction 

 of the species. They are tiny protoplasmic bodies, generally 

 oval in shape, and with few exceptions, actively motile, either 

 when liberated, or at some later period previous to germination ; 

 their movement is imparted by cilia, the lashing motion of 

 which is too rapid for observation. 



