SYMPTOMS Of^ DISEASE IN PLANTS. 237 



stimulating effect of their fungus guests. The twigs, petioles and leaves 

 of our common ash often show orange-colored enlargements, due to the 

 growth of the cluster-cup stage of a rust fuhgus. The vegetative parts 

 o: plants, as stem, leaves, and roots, often exhibit peculiar enlargements, 

 but most of these may be considered under the head of excrescences 

 and malformations. 



It sometimes happens that a parasitic fungus produces a new structure 

 which takes the place of some normal organs of the plant, as in the 

 so-called "ergots" of our wild and cultivated grasses and rye. These 

 ergots are horny, resting bodies or sclerotia of the fungus that occupy 

 the same position as the kernel or seed, and appear only with the 

 destructioh of the seed-producing structure. These ergots not only affect 

 the seed production of the host plant, but they contain poisonous prin- 

 ciples which produce serious disease when ergot-infested hay is fed 

 to cattle. 



The production of "mummies" is another characteristic symptom of 

 disease in fruit trees. Apples that are badly affected with either brown 

 rot or black rot often dry up slowly and remain hanging on the tree 

 over winter in a more or less hard shrivelled condition. These mum- 

 mies at the end of the winter period of rest may produce a crop of 

 spores which will spread the disease. This spore production may take 

 place while the mummies are still "hanging on the tree or on fallen 

 mummies. The formation of mummies is especially common in plums 

 that are affected with the brown rot. It must be at once evident that 

 mummies should be destroyed in order to prevent production of new 

 crops of spores and thus to lessen the ravages of these rot-producing 

 diseases in an orchard. The practice of allowing rotting plums to fall 

 to the ground and remain beneath the tree should certainly be dis- 

 couraged. 



Change of position is a symptom of disease that is sometimes over- 

 looked. This is well illustrated in some plants which are affected with 

 a rust fungus, in the cluster-cup stage. Some of the spurges which 

 are normally more or less prostrate or creeping become erect when 

 attacked by a fungus of the kind mentioned. This same symptom is 

 present in some tree diseases, in which normally horizontal limbs or 

 branches become more or less erect. 



As a result of the attacks of a fungus parasite a complete destruction 

 of organs may result. This effect is well illustrated in the majority 

 of our cereal smuts. In the loose smut of wheat, for example, the 

 complete inflorescence is destroyed, the glumes and other flower parts 

 being reduced to a powdery mass of black material, the smut spores, 

 which finally drop away, leaving nothing but the bare central axis of 

 the head. The same effect with but little deviation may be noted in 

 the naked and covered smut of barley and the loose smut of oats, while 

 in the kernel smut of sorghum, the kernel smut of oats, and the bunt 

 ©f wheat, it is the berry alone which is destroyed, the surrounding parts 



