248 DISEASE IN PLANTS. 



etc. cause atrophy of the seeds, and numerous 

 instances of atrophied grain occur in plants in- 

 fested 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 {Ctirculio, Bruc/ms, etc.) simi- 

 larly 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. CepJius 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 inter- 

 fered 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. 



