plantation formed during the last 20 years, and consisting wholly or chiefly of Larch, which has escaped infection. Sometimes nearly every pole becomes blistered and cankered, and it has often been found necessary to clear-fell the poles at 12 or 15 years of age and replant with some different kind of tree.

This fungus is a wound-parasite, which can obtain entrance to any tree only at damaged parts-such as punctures made by insects (principally treelice and the mining-moth), hail, straining of the branches during gales or bending under pressure of snow or ice, exudation of sap after late frost, nibbling by rabbits, squirrels, or voles, wounds made at time of lifting or setting the plants, or from any other cause whatever. Of all such causes, probably the Larch-aphis is most to blame. It is quite certain, however, that some sort of wound is necessary before the fungus-spores can effect their entrance; and of course such opportunities are most frequent where the bark is thin and tender, and where sap and resin are most likely to exude. On wound-surfaces of any sort, however, the spores find a favourable germinating bed, from which the mycelium penetrates into the cortex during the non-active period of winter rest. Its growth is checked, whilst the Larch is in active vegetation, by the formation of a tough corky layer around the blister; but during the following autumn the mycelium again penetrates from the cambium into the bark, and enlarges the canker-spot. If this should finally extend all round the stem the whole of the upper part of the tree of course dies, though otherwise the struggle of the tree for existence may often be continued for very many years. But in large cankers the mycelium usually penetrates through the medullary rays into the heart-wood, and assumes proportions interfering greatly with the circulation of the sap; and when this takes place the tree begins to sicken and die. There is always danger of wind-break at cankered spots. Where large stems or thick branches are cankered, the remains of a dead branch or twig will almost always be found in the centre of the depression. This therefore shows that infection must have started near some strained or injured branch.

Dry, warm, breezy situations are not favourable to the ripening of the sporophores; while humid protected localities favour the maturing and germinating of spores. The disease is always most frequent in pure Larch crops,

years seem to have escaped this destructive disease. In many cases small plantations of pure Larch of 12 to 20 years old have been absolutely ruined; but the canker is also frequent in mixed plantations of about 7 to 10 years of age in which woodbine has been allowed to twine round and sink deep into the bark of young stems.-This is simply the effect of trying to grow Larch under different conditions from those which obtain in its alpine home, where its natural habit is to occur only as individual trees or in small family groups interspersed among other kinds of trees. Grown pure or forming the bulk of a plantation, as has been the tendency to grow it during the last 30 or 40 years, this has certainly rendered it less capable of resisting the insidious attacks of the canker-fungus, while the damp and comparatively mild climate at the same time favours the increase and spread of the disease.-Larch disease is comparatively infrequent in Co. Wicklow. This is attributable to the fact that the Larch has usually been grown here either interplanted among Oak scrub or else in mixed plantations along with a large proportion of Scots Pine, and sometimes also Spruce and Silver Fir.

and whenever the plantations are very thick. Artificial infection succeeds most easily in the month of May; and natural infection may perhaps also be most frequent then, because well-developed ascophores are then most abundant, injuries from insects and late frosts are also frequent or very recent, and there is a strong flow of sap which oozes to the surface of young shoots on the slightest puncture being made in the epidermis. In the sap exuding through any such chance wound, the spores, floating in the air after being discharged from the ascospores, can be caught, and may then germinate and effect their entrance into the living tissues.

Damp close localities, and low-lying undrained tracts where mists prevail and late frosts are frequent in spring, are specially favourable to the spread of the disease. Its prevalence in our woodlands is mainly due to our mild damp climate favouring a very luxuriant development of the fungus. The Peziza is, like the Larch, indigenous to the Alps; but the fruits of the fungus generally dry up there without ripening, while at the same time the Larch is very much better able to resist the parasitic attacks, because there is no doubt that the long alpine period of winter rest, with the short hot summer and little or no spring or autumn weather, likewise gives the Larch a hardier constitution than it acquires in our milder climate with a long, damp, variable spring. Here the Larch is more or less predisposed to any disease, and at the same time the fungus has very favourable conditions for its vegetation.

The first signs of the disease are smooth shining spots or slight swellings which appear on the stem or branches; then the bark splits and a slight outflow of resin takes places from the fissures. This fissuring of the bark soon becomes more general, bits of bark begin to scale from the stem, and small round or elliptical cup-shaped apothecia with felty white or grey edges and bright orange-red or yellow centres make their appearance at the fissures. The dead diseased parts gradually grow scurfy and black, while the canker wounds deepen as the bark curls up at the edges of the fissures, and gradually spread up and down and round the stem, killing the pole outright in the latter case.

Life-history. When spores settle and germinate on wound-surfaces the manybranching septated hyphe of the mycelium (which are only visible with a microscope) spread quickly in the soft cambium, growing partly in and partly between the cells and the sieve-tubes, browning and killing the tissues and penetrating the wood by the medullary rays and even entering the pith. The dead bark-tissue in summer becomes shrunk and depressed, and is separated from the living bark by an unusually broad layer of cork; but the mycelium (which is only capable of growing during the winter period when the Larch rests from active vegetation) in autumn makes its reappearance from the cambium or the woody-tissue, re-enters the living bast, and gradually, year after year, increases the size of the cankerspot. The cankered or blistered part is generally marked by an outflow of resin, which soon oxydises and becomes blackened; and there is usually a deep, and each year gradually deepening, depression in the middle where the oldest tissue has been first of all killed, while the stems become hypertrophic laterally.1

1 "The tree endeavours to prevent a further spread of the parasite into its tissues by surrounding it with a thick wall of cork, but this barrier is of little use, since it can

Soon after the death of the bark-tissue the young sporophores appear as small yellowish-white pustules, about the size of a pin-head, round the edge of the blister. In a dry atmosphere these shrivel up and die; and it is only during continuously damp weather that these can ripen in August or September into the characteristic round or elliptical, white- or grey-edged, orange-yellow or orangered Peziza-cups (ascocarps), varying up to about of an inch in diameter. These cup-shaped ascocarps also often appear on the dead bark, even when there are no blisters there.

In young plantations the ascocarps are produced in large numbers near the ground, where grass and weeds keep the soil and the foot of the little stems constantly damp, so as just to provide the conditions most favourable for the conidia or preliminary fructifications ripening into the mature spore-bearing ascocarps. And as this is just the part at which plants are liable to get slightly damaged when being lifted from the nursery or at time of notching or pitting the plants, this accounts for the disease being very prevalent in young plantations. Another common point of infection is in the angles of branches and twigs, where moisture collects, and where any strain from wind, snow-pressure, &c., can most easily rupture the bark and permit the entrance of the spore-tubes of germinating spores.

Prevention and Extermination.-When once infected, a cankerous tree never gets rid of the disease. Hartig found Larch-trees on the Alps on which the canker could be counted back for 100 years; but in our damp mild climate death usually ensues long before that time. And it is seldom indeed that any except purely ornamental specimens of Larch are ever here found of that age. As stems or branches infected always help to spread the disease, diseased poles or trees should (wherever practicable) be cut out and utilised, as the risk of infection ceases soon after the tree dies and dries up. Diseased branches should be removed from the woods, and either utilised or else burned. The cleaner that plantations are kept, and the more regularly and freely they are thinned, the less favourable are the conditions for the spread of the fungus.

Pure Larch plantations formed now in any part of Britain, even on dry, lofty, breezy situations, are almost certain to be attacked, so ubiquitous has the disease become; and the only way of securing even partial immunity is to grow Larch only in admixture with other trees, and preferably only among broad-leaved species (Beech, if possible). Forming mixed woods of Spruce and Larch is more likely to spread the disease than to prevent it, if the Spruce gall-aphis should happen to be in the vicinity (see p. 131). In ornamental trees the blister may be cut out with knife or chisel and the wound treated antiseptically with tar. Scrubbing canker-spots with an antiseptic solution (see pp. 106, 140, 156) has also been found cheap and effective for interspersed Larch (2s. 6d. to 3s. an acre; Gayton Hall estate, Ross-on-Wye, Herefordshire).

only be formed in the living bark, and the fungus can therefore gain access to the living tissues beyond through the wood. During the summer the fungus is held in check by the vital activity of the living cells and the cork layer, but when the tree has passed into the resting condition, and those cells have become dormant, the spread of the mycelium is unhindered, and the fungus is then able to increase the area of the blister. In this way the struggle goes on between the host and parasite from year to year. The cambium round the diseased area keeps on forming new annual rings, so that ultimately the canker appears as a flattening, or as a depression in the stem. The supply of food is diverted to the side remote from the blister, with the result that the cambium there, being better nourished, forms broad year-rings, thus causing a projecting or swollen part on this side. The tensions which are set up between the living and dead tissues cause ruptures here and there, which are followed by an outflow of resin."-(Borthwick in Trans. Roy. Scot. Arbor. Socy., 1903, p. 39.)

The Japanese Larch (Larix leptolepis) has up to the present appeared far less liable to the attacks of the canker-fungus, the Larch-aphis, and the mining-moth, than the European species. But it is by no means immune from infection by this fungous disease, nor from the attacks of these two insects, which certainly predispose trees towards infection and produce the necessary wound-surfaces enabling the fungus to enter the living tissues.

2. Peziza (Dasyscypha) resinaria, the Spruce Blister or Canker, produces a disease very similar to the above. It is local in its distribution, and is most frequently found attacking Spruce in Central and Southern England. But it is also not uncommon on Larch, occurring either alone or along with the true Larchcanker; and it has recently proved very destructive to the Pinus excelsa in Wiltshire (Massee). Even when examined with a pocket-lens, it requires some practice to distinguish it from the Larch-canker fungus. This being so, attacks of P. resinaria may often be attributed to P. Willkommii, in which case this may be a more destructive disease than has hitherto been suspected.

P. resinaria is, like P. Willkommii, purely a wound-parasite, which can only enter the living tissues through wounds made by insects, wind, &c., or by another minute parasitic fungus, a species of Erosporium. About three months after becoming infected with Exosporium, fruits appear as numerous small black dots on the surface of the bark, which becomes fissured with narrow cracks filled with resin; and through these resin - filled cracks the germinating spores of Peziza resinaria are enabled to enter the living tissue of the tree.

After infection the outer bark soon breaks up and scales off in fragments through the pressure exerted by the inner bark becoming rapidly hypertrophied. With age the original depression made in the bark grows larger, but there is more swelling round the edges of the wound than with the Larch-canker, and the wound more frequently completely rings and kills the branch attacked. The flow of resin is also much more copious, and large pockets form in the wood, which become filled with hardened resin permeated with the mycelium. Resin-ducts form in large number in the wood near the wound, and the resin also often fills the cells lining them.

The ascophore or cup of this fungus is somewhat smaller than in Peziza Willkommii, and is more distinctly stalked. The disc is always yellow or pale orange, not orange-red; and externally it is white or greyish-white, and appears minutely velvety when examined with a pocket-lens. The immature conidia are small, elliptic-oblong, and of a dull orange colour. The spores are subglobose and much smaller than those of P. Willkommii.

Peziza (Dasyscypha) subtilissima, a closely-related species, also sometimes attacks Silver Fir and Larch in Britain.

(b) The genus Sclerotinia.

The genus Sclerotinia occasions several minor diseases on trees. From the sclerotia the sporophores or stalked cups characteristic of the Peziza family are produced if the air is sufficiently moist. Sclerotinia betula deforms the fruits of the Birch, and makes them heart-shaped in place of elliptical. S. alni does the same on the Alder, and also attacks the fruit of whortleberries. S. aucupariæ immunifies the fruits of the Mountain-Ash, and S. padi those of the wild Cherry.

3. But of far more importance to the forester than any of these is Sclerotinia Fuckeliana, because its conidia-form Botrytis cinerea, the common grape-mould, which is usually only a saprophyte, can during wet spring and summer weather become parasitic and very destructive. It then attacks the foliage and young shoots of Douglas Fir, Silver Fir, and Spruce, and some

times also Larch and Pine. The previous year's shoots, too, are sometimes attacked in the Silver Fir. This fungus was at first thought to be a separate species (B. Douglasii), but it is now known to be as above described.

As a saprophyte it is everywhere to be found (like Lophodermium pinastri, see p. 160) infesting dead foliage in conifer woods; and if such litter be used for covering seed-beds and nursery-lines, then parasitic infection is only too likely to take place. Botrytis cinerea then causes a very destructive disease in nurseries, and many of the deaths occasioned in seedling-beds or nursery-lines, and attributed to frost, &c., are perhaps really due to this fungus. The parts infected are the top-shoots of seedlings and the tips of the lower branches of older plants and trees. The diseased shoots become twisted or curved downwards, and the leaves die off, though often still held by the brown cobweb-like mycelium.

It also attacks Larch, Scots Pine, and Wellingtonia seedlings, the leaves soon turning yellow and dying off, when they hang down, supported by the mycelial threads. It is probably chiefly due to this fungus, and perhaps also to Lophodermium pinastri, that enormous numbers of self-sown Scots Pine seedlings are killed year after year, making it now in many localities difficult to effect natural regeneration satisfactorily. It also sometimes attacks and destroys the leading-shoots of Douglas Fir plants in young plantations, more especially in those at low elevations and in humid localities.

Life-history. If the spores alight on young leaves or shoots in damp weather, they soon germinate and enter the tissue. The mycelium penetrates intercellularly in the leaves and the young shoots, killing the tissues as it proceeds. Sporophores and sclerotia are formed, and the spores can remain dormant for a long time and then germinate when conditions are favourable. On germinating, however, the spore-tubes cannot pierce the bark of a 2-year-old seedling, except at a wound-surface caused by late frost, insects, &c., when the fungus destroys the cambium and kills the plant, the bark forming a loose sheath round the stem. Plants attacked in the nursery are always unfit for use, as the damage caused makes them bushy and stunted, and destroys the leading-shoots.

Prevention and Extermination.-As the Botrytis grows saprophytically on all kinds of dead and parasitically on dying plants, it is of importance to keep the nursery-beds clean by weeding. It spreads most abundantly in humid air, so that nurseries should not be made in damp spots.

The best way of preventing its spread is to spray frequently with "Violet Mixture," consisting of 2 lb. sulphate of copper, 3 lb. carbonate of copper, 3 oz. permanganate of potash, lb. soft soap, and 18 gallons of rain-water (the soap being dissolved in hot water). All the infected ground, and for some way beyond that, should be thoroughly wetted.—(G. Massee, in Jour. of Board of Agriculture, vol. x., 1903, pp. 17-20.) See also Agri. Leaflet No. 127 (Sclerotium Disease.)

(c) The genus Cenangium.

4. Cenangium abietis is usually only saprophytic, but can also become parasitic and do a considerable amount of damage. It chiefly attacks Austrian and Corsican Pine of 5 years of age or older (never younger plants), and causes their shoots to shrivel up; but only weakly individuals become infected. Infection only takes place during the winter period of rest from active vegetation. The mycelium grows chiefly in the bark, and in the following spring causes the death of the last year's shoot and the terminal bud. Before this takes place the needles