Any form of defoliation--_e.g._ excessive plucking of tea and mulberry leaves, browsing of animals, etc.--exposes the twigs to the dangers of dying-back, the accessory phenomena being similar to those already described. _Stag-head._--Old trees, though vigorous and in full foliage throughout the crown generally, frequently lose the power of bearing leaves on their topmost branches and twigs, which stand out bare and brown, and fancifully resemble the antlers of a stag: hence the forester's name "stag-head." This "top-dry" condition is frequently due to the removal of litter, or to excessive draining, or to the roots having gradually penetrated into unsuitable soil. The consequence is that some dry summer the drought causes the breakage of the water columns above, and the twigs die back. Tropical trees may also become _stag-headed_ owing to the attacks of _Loranthus_ and other parasites, the portions above the point of attachment dying back from inanition. Cases also occur in the tropics where the _stag-head_ condition is due to the persistent roosting of frugiferous bats--"flying foxes"--which tear the bark and foliage with their claws, and befoul the twigs generally. NOTES TO CHAPTER XXVI. The principal literature as regards frost is given in the works of Frank, Sorauer, and Hartig already referred to. An excellent summary will be found in Hartig's _Diseases of Trees_, p. 282, and in Fisher "Forest Protection," Vol. IV. or Schlich's _Manual_, p. 423. CHAPTER XXVII. MONSTROSITIES AND MALFORMATIONS. _Monstrosities--Teratology--Atrophy of organs--Shanking of grapes--Barren fruit trees--Dwarfing--Distortions and malformations--Fasciations--Flattened roots--Torsions--Curling and puckering--Leaf rolling--So-called "spontaneous" teratological changes._ _Monstrosities._--In a wide sense this term is applicable to many cases here treated under other headings, and signifies any departure from the normal standard of size, form, arrangement, or number of parts, and so forth, due to arrest of growth, excessive growth of parts, or of the whole organs, etc.