58 THE SAPROLEGXIACEAE 



proliferating from the side below as in Achlya; when growing through 

 others sometimes discharging spores through the side wall of the old 

 sporangium; spores 9-11.551, tfeick, in our form swimming in two stages as 

 usual in the genus (not swimming in Huxley's form — see below). Sexual 

 reproduction not observed so far in our form and very rarely observed 

 by others (Huxley). Received by us from the fish hatchery at Wythe- 

 ville, Va., and from the aquarium of the U. S. Fish Commission in Wash- 

 ington, in each case growing as a parasite on fish. 



There is every reason to think that this is the same as the sterile 

 Saprolegnia that has been reported so often as causing (or appearing 

 with) a well-known diseased condition of fish. The disease is apt to 

 appear at any time on young fingerlings in fish hatcheries or on the eggs 

 and may at times be a serious pest. It is also apt to appear now and 

 then on gold fish and in fish pools and aquaria and sometimes causes 

 (or accompanies) epidemics of disease which result in great mortality 

 of salmon, trout, etc., in the free waters of rivers and lakes. 



That the species is almost or quite without oogonial reproduction 

 is evidenced by the fact that only very rarely have oogonia been reported 

 (and then without proof that they belonged to the parasite), notwithstand- 

 ing the fact that this species has been more studied perhaps than any 

 other of the family. The plant was for a long time carelessly spoken of 

 as S. ferax, but in the few cases of sexual reproduction observed there 

 is a close similarity to that of 5. monoica. This resemblance is so close 

 in fact that Huxley, who was the first to report the oogonia (Quart. Jour. 

 Mic. Sci. 22: 311. 1882), considered it S. monoica (S. ferax \ar. monoica, 

 he called it). Nevertheless we do not think we are justified in consider- 

 ing the (at least practically) sterile parasite in question the same as 

 the well-known and abundantly fruitful saprophytic 5. monoica, even 

 though they are much alike in other respects. The tendency to 

 proliferate from the side below, as in Achlya, is from our observations 

 even more strong in this species than in S. monoica. Huxley reports 

 that in his plant the spores did not sivini on emerging but floated pas- 

 sively. Our plant does not show this character (if indeed it is a per- 

 manent character in any form, which is more than doubtful), the spores 

 swimming as usual in the genus. It is interesting to note here the 

 similar suppression of a swimming stage in Achlya aplanes which is other- 

 wise very like A. prolijera. 



For comparison it will be of interest to refer to Rothert's remarks 

 on a Saprolegnia found by him on fish eggs (called S. sp. I) and probably 

 the same as this. He says (1888, p. 295) that although the plant was quite 

 free from parasites and was cultivated for a half 3'ear in various conditions 

 he was not able to induce the formation of oogonia. That so far as 



