244 Proceedings of the Royal Society 
Suppose an oospore (resting spore) to be capable of producing, 
under favourable 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 greyling caught by 
Mr J. Willins, student of medicine, when angling in Keerfield Pool 
in the Tweed, near Peebles. It had been cut in two halves and 
the tail portion 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 short jerks, not by a continuous move- 
ment. 
Those zoospores were pyriform in shape during the short time 
they were observed in motion ; on becoming stationary the cilia dis- 
appeared, being probably withdrawn into the body of the spore, 
which then assumed a globular form. This change took place in a 
very short time — not exceeding ten minutes, — and while under 
observation minute projections became visible on the edge of the 
spore, which grew into delicate filaments of considerable length. 
I have succeeded in fixing the development of the fungus in this 
state, and it can be seen in various stages of growth, all of which 
were ciliated spores within the space of one hour. 
This, the asexual mode of propagation, is remarkable for the 
rapidity with which it is accomplished. A few of those ciliated 
spores become attached to any part of either a healthy or a diseased 
