Atrophy is a common phenomenon denoting dwindling or reductions in size of organs due to insufficient nutrition, or arrest of growth from various causes.
Atrophy of leaves is a common result of the attacks of parasitic fungi, even when the latter induce local hypertrophy - i.e. excessive growth of particular parts, e.g. Synchytrium on Dandelions and Anemones. Puccinia suaveolens causes partial atrophy of the leaves of Thistles, Aecidium Euphorbiae of those of Euphorbia.
The carpels of Anemone are atrophied in plants attacked by Aecidium, and the whole flower is suppressed in Cherries infested with Exoascus Cerasi, while other fungi - e.g. Cystopus, Exoasci, etc. - cause atrophy of the seeds, and numerous instances of atrophied grain occur in plants infested with Ustilagineae.
Atrophy of the grains of cereals is sometimes due to the direct attack of animals, e.g. eel-worms (Tylenchus) eat out the grains of Corn; weevils and other beetles (Curculio, Bruchus, etc.) similarly devour the contents of grain and nuts, the flowers of Peas and Apples, and so forth, inducing atrophy of the parts left. Still more striking cases are afforded by small insects which bore into the halms of cereals, and cause atrophy of the whole ear - e.g. Cephus in Wheat and Rye. Barley occasionally withers after flowering, the grain atrophying from no known cause, terms like consumption given to the disease conveying no information.
Atrophy of young fruits is commonly due to the flowers not setting - i.e. some agent has interfered with the normal transference of the pollen to the stigma. This may be due to excessive rain washing out the pollen (e.g. Vine), to a lack of the necessary insects which effect pollination, often seen in greenhouse plants; to the stamens being barren - e.g. certain varieties of Vine - or to the premature destruction of the stigmas by frost, as in Cherries, Pears, etc., or by insects, as in Apples, or fungi, e.g. the infection of bilberries with Sclerotinia; or even by poisonous gases, as is sometimes seen in Wheat, etc., growing near alkali works. Drought is also a common cause of atrophy of young Plums.
Shanking of Grapes is a particular case of atrophy and drooping of the immature fruits, due to the supplies being cut off by some agency. It may arise from very various causes which bring about disease in the leaves or roots, and should always be looked upon as a sign of weakness in the Vine, the structure of which is affected, eg. poor wood - or the functions interfered with, eg. water supplies deficient owing to paucity of roots.
Barren Apple, Pear, Plum, and other flowers are often found to have been bored through the petals while in bud, and the whole "heart" of the flower eaten out by the grubs of Anthonomus, leaving the unopened buds brown and dead, as if killed by frost or drought, and often erroneously supposed to be so.
The wilting and shrivelling of Clover is sometimes due to Sclerotinia, the mycelium of which pervades the roots and stock, on which the sclerotia may be found. Lucerne is similarly killed in Europe by the barren mycelium of Leptosphaeria, which may be found as a purple mat on the roots.
Dwarfing consists in partial atrophy of all the organs, and is a common result of starvation in poor, dry, shallow soils, as may often be seen in the case of weeds on walls or in stony places. Dwarfs which are thus developed in consequence of perennial drought are not, however, necessarily diseased, in the more specific sense of the word; their organs are reduced in size proportionally throughout in adaptation to the conditions, and simply carry out their functions on a smaller scale.