them appear too highly coloured. Certainly in the early spring many kelts were still in the river, and were in a very bad state of health to begin with. The skin would be rubbed off their noses and fins with making gutters in the gravel wherein to deposit their eggs; the male fish would often have sores through fighting, and in every way would be in as suitable a condition for receiving the spores of Saprolegnia as could possibly be found. As a matter of fact, the fungoid growth is observed on the salmon after every spawning season. It was only its unusual virulence last spring which caused so much alarm. Then the disease was seen at its worst and under complicated conditions; but the fungus had nothing to do with making the sores-they were there already. It might aggravate them, perhaps make them larger, but the sores themselves were no more due to the fungus than to the water in which the fish lived.

Mr Stirling is of opinion that the fish do not die of the fungus, but of the injuries they inflict in trying to rid themselves of the pest, and quotes, in corroboration of his views, a letter by Commander Duncan Stewart, R.N., published in the "Field" of 25th May last. It is quite natural that, with sores all over them, the fish should be pained by the growth of the mycelium threads of the fungus under the skin and amongst the flesh. I do not doubt that many fish killed. themselves, or at any rate might have done, in their agonising struggles to rid themselves of their pain. This was the early and most noticeable stage of the disease; but nothing is said of the usual form, which became more prevalent when the kelts had either died or returned to the sea, but which proved no less fatal. Many a fish I have seen without a scale displaced, and yet as certainly in the clutches of death as could possibly be; rolling over and over as it was washed down by the stream, or floating heedlessly about in some backwater, allowing you to touch it without a struggle. This is the nature of the disease as I observed it in April last, and this is its usual form in confinement. There was no struggling or writhing about, and presumably no pain. In the "Naturalist" for May last I described the gradual development of the fungus over the head and gill covers of the fish; how that, on opening the mouth of a recently dead fish, "you will find the throat completely

stopped up with fungus, and the inner surfaces of the gills laced with its filaments. The blood is quite black, and it is evident the fish has died of suffocation." I came to this conclusion from watching the fish in the river, and have since had my views strengthened by observations on fish in confinement. On the 3d of May I received several chub to experiment on, and the following extract from my journal will show the result:

May 5th.-The chub had been placed in a tank with weed and pebbles from the Esk, and with a good stream of water running through it. This afternoon I noticed one with its right pectoral fin damaged. It appeared to be a little white near the joint, and I suspected fungus. The tank had been cleaned out before the fish were placed in it, and the bottom covered with sand and gravel, with here and there a weed. The water was filtered through wool.

"May 7th.-It was now evident that the fungus was developing on the wounded fin, but it did not appear to be developing quickly longitudinally. It had, however, spread to the base of the left pectoral fin.

May 9th.-Ever since the fish took on' it has been remarkably sluggish, but to-day particularly so. I several times held it in my hand and it would give a slow stroke with its tail, but not struggle hard to get away. I opened one gill cover and saw that the fungus filaments had spread to the gills.

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May 10th.-At breakfast time my chub was dead. As it lay in the water I could see the fungus filaments floating from its mouth. I found the mouth quite stuffed with fungus, and the blood was black-thus, like the salmon, it had died of suffocation. In this case, about 5 days had sufficed to kill the fish after the fungus had got established, so that a Correspondent was wrong when he accused me of giving the fish too little time to die in. It appears to be a question of how soon the fungus gets to the gills, and yet I fancy I have seen dead fish without a bit of fungus on the head."

Here there was no sore, and the only patch of fungus visible on the fish was that between the pectoral fins. This corresponds with the later stage of the disease in the Eden when there was scarcely a kelt left, and every fresh-run fish was attacked within a few days of its arrival. This I take

to be the normal action of the fungus, the other and more violent form being aggravated by other circumstances.

That Saprolegnia can kill a fish in a very few days is further confirmed in a paper by Mr F. B. Hine in the "American Quar. Micros. Jour." No. 1. This paper, I may say, is written without reference to any particular species or disease, and is a record of observations on the Saprolegnieæ. With regard to the rapidity of growth, Mr Hine says, “In one case zoospores were placed upon a slide, with a small fragment of a fly, the first sporangium opened in about thirty hours, and the second one, on the same filament, eight hours later.

With regard to the manner in which the disease is communicated, the following experiments, conducted in two separate seasons, with the same results, by Mr J. T. Carrington of the Royal Aquarium, Westminster, will be of interest. He has nine hatching tanks arranged into sections of threes, two being below the upper section, and the water circulating through the series from tank No. 1 to tank No. 9. The tanks were stocked with young trout of various species. In these tanks Mr Carrington tried several times the effect of overcrowding; this induced the fungus to some extent, but, so long as they had plenty of water, the young fish were not badly attacked. He then tried short supply of water, and the result was an immediate and serious attack of fungus. The disease could not be produced by infection, but by contagion it could be introduced into any particular tank. The trout in tanks Nos. 1 and 2, which secured the first clean water, were severely attacked by the fungus, but although the same water in which they lived passed on to Nos. 7, 8, and 9, the fish in these latter tanks were not affected. It could not be because they were of a different species, for healthy fish were removed from tanks No. 1 and 2 to 7 and 8 and were not affected. Thus it would appear that, as a rule, even in young fish, some predisposing cause, such as a short supply of water, and particularly overcrowding to such an extent as to permit of contagion, is necessary for the spores of Saprolegnia to develop successfully on them, and that, so long as the fish remain healthy, the presence of Saprolegnia spores in the water is of little

consequence.

The fungus appears to develop sooner in still than in running water, but owing to the accumulation of decaying animal matter in small still-water tanks the fungus does not last long. In running water, however, I have kept Saprolegnia ferax for five months, and it is at present in as healthy a condition as when I got it.

In confinement, salt-water, or salt thrown into fresh water, will check the development of the fungus, and fish not badly attacked will get better; but the salt does not destroy the fungus, it seems to act as a preservative. I placed a dead minnow affected with fungus, and one not so affected, in a beaker of sea water, and, for comparison, placed a diseased minnow in a beaker of fresh water alongside. The water was changed in each every two or three days. Up to the time of the fish being so decomposed as to fall to pieces when the water was agitated, no further development of fungus was noticeable in the beaker of salt water, while the minnow in the fresh water had become covered with a mat of fungus. I am very sorry to find that the disease is still at work in the Eden, though the scarcity of fish makes it less noticeable.

II. The Exact Measurement of Trees.
CHRISTISON, Bart., V.P.R.S.E., &c.

(Read 12th June 1879.)

By Sir ROBERT (Part 2.)

In the observations on this subject laid before the Botanical Society last year, it was stated that a number of trees had been measured in the spring according to the recommendations there given, in order to ascertain whether minute measurement may be relied on for determining relative growth for short periods of time in varying circumstances. The measurements having been repeated at the close of the growing season last year, and again at the beginning of it this year, it may be well that the results, though they must be tested by the experience of another season of growth, should be now communicated to the Society; as others may be thus encouraged to take up what appears likely to prove an interesting line of inquiry.

Last summer and autumn happened luckily to be favourable seasons for tree-growth. The previous year was exceptionally the reverse. In 1877 almost continual cold, cloud, damp, and frequent rains prevailed in Scotland

generally all summer and autumn till the middle of September. As illustrative of the effects, it may be mentioned that around Arrochar, close on the sea-level, I found in the middle of August the wild plants of midsummer still in flower; that in the beginning of October there was scarcely a ripe bramble-berry to be seen, but on the other hand no want of flower; that at the same date the acorns on the natural oaks of Loch Long and the neighbouring Loch Lomond were no bigger than a pin's head; and that the acorn did not ripen, or even attain a greater size, either there or in Mid-Lothian, Dumfriesshire, or any other part of Scotland from which I obtained authentic information. As another consequence of that most unpropitious season, the young wood of the year's twigs could not duly ripen in the autumn. This unfavourable preparation did not seem to have any injurious influence either on the flowering or foliage of trees and shrubs in the following year, 1878. But in many of them it impaired greatly the

passage from flower into fruit.

The early part of spring 1878 commenced favourably,— indeed, only too soon. Subsequent cold retarded progress much; so that May had advanced far before trees began to put on their green livery. But as the cold was never considerable, the buds, which began to show dangerously soon, were not frost-bitten; and consequently the foliage on all trees became eventually very rich and dense. I observed however that, in the case of many forest-trees, the flowers fell without forming fruit; and the late Mr M'Nab mentioned to me that he had made the same observation wherever he happened to be in the flowering season.

The month of May last year was cool and dry; but there was no want of sunshine. Subsequently the weather was sufficiently warm, with much sunshine, a clear atmosphere, occasional light showers, and few rain-storms, from the end of May till the end of October; and even during the whole month of November there was little frost, none of any consequence even during night, and none which lasted long after day-light.

Taking all these circumstances into account, the safety of budding in the spring, the genial summer and autumn, and the late arrival of the winter's frost, 1878 must appear to have been favourable to the growth of trees. It cer