FUNGUS DISEASE AFFECTING SALMON AND OTHER FISH. 533 



in more or less active couditiou. It is believed that tliis fuiiguK has 

 two modes of reproduction, namely, by oospores and by zoospores. The 

 oospores are few in number, and may be looked upon as ova, and they 

 required sexual impregnation. They are called resting spores, from a 

 belief that they remain dormant in the water for an indefinite period, 

 which may continue for many years ; and during this phase of their life 

 they may germinate in limited numbers, providing only for the contin- 

 ued existence of the species. While in this state of abeyance there is 

 DO plague of fungus, from the ova only producing neutral or barren 

 plants, which bear no fruit or seed. After a period of longer or shorter 

 duration, a season, or a series of seasons, may follow, during which an 

 unknown intluence arises which acts upon the resting spores, by which 

 they are stimulated to great reproductive energy, and the plants they 

 produce being fruitful, the asexual mode of reproduction commences. 



The zoospores are produced in pod-like cases called zoosporangia^ 

 which are situated at the apex of the filaments, and may be looked upon 

 as fruit or seed. They are the ciliated spores and are the media by 

 which the fungus is communicated to the fish. The zoospores are pro- 

 duced in great numbers, each zoosporangium containing from 100 to 150 

 of them. The oospores or ova are produced in a globular sack, which 

 forms at the root-ends of the filaments or upon the roots themselves. 

 Those sacks are called oogonia, and each sack contains a few oospores or 

 ova, three or four to nine being the numbers I have observed in the four 

 instances in which I have seen them in the whole courses of my investi- 

 gations. 



Suppose an oospore (resting spore) to be capable of producing, under 

 favorable circumstances, a plant carrying 100 filaments, and each of the 

 filaments to produce 100 zoospores, 10,000 germs would be derived from 

 a single ovum or resting spore, every one of those germs being capable 

 of producing a plant as productive as that from which it derived its 

 existence ; a multiplication of innumerable millions would be produced 

 in a few days, the ciliated spores being as plentiful in the water as snow- 

 flakes are in the air during a snow-shower ; and in this way the plague 

 of fungus, the so-called salmon disease, is originated. 



I obtained in April the living fungus from a grayling caught by Mr. 

 J. Williams, student of medicine, when angling in KeerfieldPool in the 

 Tweed, near Peebles. It had been cut in two halves and the tail por- 

 tion selected ; it was packed in a tin vessel with wet moss, which had 

 preserved the fungus in active vegetative growth, when I received it on 

 the morning after its capture. A pale pink bloom was plainly visible 

 over the whole surface of the matted fungus, and, when it was held up 

 between the eye and the light, a new growth appeared to cover the older 

 fungus on its outer surface to about one-eighth of an inch in height. 



When examined under the microscope in water, free ciliated zoospores, 

 which had escaped from the zoosporangia situated at the extremities of 

 the filaments, were observed in motion ; they moved in a fitful way, by 

 shorts jerks, not by a continuous movement. 



