58 The Fungus of Salmon Disease. 



similar life) a seed, or, as it is usually called, a spore. These 

 seeds, when existing in a water, are always seeking fitting soil 

 to grow upon, and when they find such a nidus they germinate 

 and take root. If the place where they start into life is favour- 

 able to them, and the nourishment they find there of a suitable 

 kind, and in plenty, they develop freely, and continue grow- 

 ing until the supply of food is exhausted, or until some un- 

 favourable condition arises to prevent their further develop- 

 ment ; but it would be rare in an open water, and more 

 especially in a river, for an unfavourable influence to overtake 

 them unless artificially produced ; and so, while growing, they 

 rapidly produce and mature their own seed, which, when the 

 plant flourishes, is being continually liberated into the sur- 

 rounding water, and there distributed, to be again planted 

 on the nearest soil obtainable, where the re-production continually 

 goes on. Thus a water may become charged with the spores 

 of the disease, each and every one of which is ready to develop 

 on the shortest notice and carry on its destructive function, 

 when such a food as the epidermis of living salmon presents a 

 favourable ground for it. 



Salmon disease, as you are no doubt aware, is a fungus, or 

 low form of plant life, of the genus known as Saprolegnia ; the 

 particular kind with which we have to do belongs to the 

 Saprolegnia ferax group, of which again there are three recog- 

 nised forms, named Torulosa, Monoica, and Thureti. 



The life history of several families of the Saprolegnieae was 

 very carefully worked out by Cornu nearly twenty years ago, 

 and many of the most famous of the later German, French, 

 and English biologists have paid much attention to the subject, 

 and from time to time published their researches ; the latest 

 original papers on the Saprolegnieae coming from the pen of 

 Professor Hartog, of Queen's College, Cork. 



It is known that salmon disease is generally propagated from 

 zoospores, which are the ordinary everyday seed of the plant. 

 These spores, like grain, are matured at the extremity of their 

 stems, or hyphae, in an enlargement called a sporangium, and 



