by frost, weight of snow, insect punctures, or otherwise, and that it is usually worst in sheltered hollows, where damp air lies and spring frosts are severely felt, and that on high situations facing north and east the disease rarely causes much injury.
All this I admit in full, but I am also convinced that, as the spores of the fungus are now so generally present everywhere, it is impossible to eradicate it, the only way by which it can be combated is by planting only on soils and in situations which experience has shown enable the tree to grow vigorously, and on poor and dry soils mixing it with hardwoods, the fall of whose leaves enriches the soil and keeps it cool and free from grass.
Heart-Rot in Larch.—Though sometimes confused with Peziza by careless observers, this is a totally different disease. C. M'Intosh[1] describes it very fully, and Hartig refers to it under the name of root-rot. Forbes believes, as I do, that it is the direct result of unsuitable soil, either too wet or too dry. It is most common on very poor limestone, sand, and chalk, but also occurs on clay and gravelly soils. In my experience it is especially noticeable where larch follows larch on soils containing insufficient nourishment, and can only be avoided by not planting larch where it is found to be prevalent. It usually attacks trees of about twenty years old, when they have got over their first period of vigorous growth and have practically exhausted the available sources of nutrition. According to Mr. Simmonds, late Deputy Surveyor of Windsor Forest, larch grown on what is called iron pan in that district gets red rot at the heart and is then said to be "pumped."
Larch Bug.—What is commonly known as larch aphis or larch bug is an insect called Chermes laricis. The life-history of this insect is at present somewhat obscure, some continental observers believing that it passes through an intermediate stage of existence on the spruce, as no males have yet been found on the larch, in which case it is evident that the insect cannot spread or become numerous unless spruce exists in the neighbourhood. But this is contested by Dreyfus, and I have observed that in England at any rate it multiplies exceedingly where no spruce are near. The females pass the winter under the bark, and are wingless, oval, of a purplishblack colour, and have a long bristle-like sucker through which they feed on the sap of the leaves. In spring they lay eggs which produce young, which grow rapidly, and are covered later by a whitish woolly down, and when numerous give the trees a whitish appearance. They increase rapidly by successive broods, and seriously weaken the constitution of the trees when young, rendering them especially liable to succumb to the attacks of Peziza, which often accompany and succeed them. Whenever I have seen bad attacks of the bug I have noticed that the Peziza is more than usually destructive, and it seems as though the climatic conditions which favour the one also favour the other. In the autumn the bark of the trees in a badly attacked plantation appeared quite black; and though this plantation was in a high situation, exposed to the east, and was heavily thinned the year afterwards, the greater part of the trees, which were thirteen years planted from Tyrolese seed, and had been growing vigorously at first, were so sickly on the thinner and drier parts of the land
- ↑ The Larch Disease (1860).
