Burrows and excavations. Bark-boring - Wood-boring - Wood fungi - Leafminiers - Pith flecks - Erosions. Skeleton leaves - Irregular erosions - Shot holes. Frost cracks - Strangulations - Spiral grooving.
Natural wounds are produced in a variety of ways during the life of the plant, and, generally speaking, are easily healed over by the normal process if the area destroyed is not too large, and the parts remaining uninjured are sufficiently provided with foliage, or with supplies of food-materials stored up in the roots, rhizomes, medullary rays, etc., to feed a vigorous callus.
The nature of such wounds and the mode of healing are explained by what we know of artificial wounds, and it only remains to point out that the principal danger of ordinary wounds is not so much the direct traumatic action, because the simpler organisation of the plant does not involve matters connected with shock, loss of blood, etc., as in animals; the danger consists, rather, in their affording access to other injurious agents, especially fungi, and the treatment of wounds frequently resolves itself into cutting or pruning in order to get clean surfaces which can heal readily.
Wounds on leaves imply loss of foliar surface - i.e. of chlorophyll action - and the remarks on page 193 apply.
Burrows may be taken as comprising all kinds of tunnel-like excavations in the various organs of plants, including those cases where insects burrow into hollow stems of grasses, etc., as indicated by the perforations they make in the outer tissues.
In addition to the notes to the last chapter, the reader may be referred to Fisher in Vol. IV. of Schlich's Manual of Forestry, Chap. VI., for an account of Hess' excellent work on Boring Beetles, etc.
The authority on Wood-fungi is Hartig, see especially his Zersetzungs - erscheinungen des Holzes, the principal results of which are condensed in his Diseases of Trees already referred to. As regards "Pith-flecks," the reader should consult Frank, Krankh. der Pflanzen, B. I., p. 212: the subject needs further investigation.