Such _teratological_ conditions are however by no means always _pathological_: that is to say, they may be variations which do not threaten the existence of the plant. In some cases they are clearly due to exuberant nutrition, and although they may occasionally predispose to disease, in others they show no evidence of doing so. The whole practice of horticulture and agriculture abounds in examples of teratological sports or varieties which are transmissible by seeds, budding and grafting, and other means--_e.g._ double flowers, hypertrophied floral organs (cauliflowers), seedless grapes and oranges, crested ferns, etc.; and even when such varieties could not live as such in a state of nature, there is evidence to show that many of them readily revert to the original seed-bearing or single condition, and adapt themselves to the altered environment. Every part of the plant may exhibit teratological changes, and I shall for the most part select cases in illustration which indicate approach to pathological states, and group with them cases known to be pathological in origin. _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.