DISEASES OF CULTIVATED PLANTS 433 



NAMING PLANT DISEASES. 



Plant diseases are named with due regard to the symptoms and 

 causes of the disease. In the case of enzymatic diseases wherein we 

 have peculiar variations or yellowing of the leaves, the names given 

 are more or less descriptive. The same applies to the diseases that are 

 caused by freezing, hail, etc. 



Parasitic diseases are named with regard to the organisms which 

 cause the disease, or to the effects they produce in the host parts, 

 that is, those diseases which result from attacks of the rust fungi 

 (Uredineae), are properly called rusts; also the smutty, dirty con- 

 ditions resulting from the attacks of the smut fungi (Ustilagineae), 

 are known everywhere as smuts; these are well known and destruc- 

 tive upon grasses and cereals. Thus we have smuts of oats, corn, 

 wheat, broom corn, sorghum, millet, blue-grass, etc. 



The anthracnoses are produced by a definite class of fungi 

 (Melanconiae). The name anthracnose is applied to a disease of a 

 given host caused by an organism of this group and the host name is 

 usually retained, as the anthracnose of wheat, the anthracnose of rye, 

 the anthracnose of raspberry, wherein the diseases are caused by spe- 

 cies of this group of parasitic fungi. However, in the case of attack 

 upon the fruit as in the anthracnose of apple, because of the bitter 

 taste given to the fruit, we have the popular name bitter-rot; in a 

 similar instance, viz., that of the anthracnose of the grapeberry, the 

 discolorations of fruit are so characteristic that it is popularly called 

 the birds-eye rot. With wheat, oats, rye, etc., the name is applied 

 because of the organisms found. As stated in the preceding pages, 

 we describe most leaf infesting diseases with regard to the effects the 

 parasites have upon the host; thus we have the leaf-spot disease re- 

 sulting from attacks of any one of a number of fungi, chiefly, how- 

 ever, belonging to the imperfect forms. The shot-hole fungus of the 

 plum is a good illustration of the naming of a trouble from the 

 symptoms produced. 



A considerable group of diseases are known as downy mildews. 

 Among these we have the destructive potato late blight and rot, 

 Phytophthora; also the cucumber disease, Plasmopara, as well as the 

 grape downy mildew and the common white molds of the mustard 

 family. The powdery mildews by reason of the appearance upon 

 the surface of parts attacked, are descriptively named mildews. A 

 definite system has been followed in most cases of naming plant dis- 

 eases and I trust the results will not be altogether disappointing. 



The differences between the species of parasitic or other fungi 

 are as strongly marked as those of higher plants, even though micro- 

 scopic examination is necessary to distinguish these characters; it 

 shows, therefore, that a discriminative system of naming diseases 

 has a secure foundation. 



THE PLANT OR HOST IN RELATION TO DISEASE. 



As stated elsewhere only closely related plants are usually sub- 

 ject to attack by a parasitic organism, thus it happens that the tomato 

 as well as the potato plants are attacked by the downy mildew or late 

 blight fungus of the potato. In general the true parasites among 



