PLANT DISEASES 



167 



studies are usually published in bulletins which furnish de- 

 tailed information in regard to particular diseases, that cannot 

 be given in a text like this. These references, as well as 

 those indicated in the appendix, should be used for further 

 study and information. Such a study will be worth much 

 more if the diseases of the plants which are common on the 

 home farm are used as a basis, 

 and through such study a 

 means of control put into opera- 

 tion. 



Common parasitic fungi. - 

 Detailed study of most parasitic 

 fungi is difficult and requires 

 special training. It is possible, 

 however, to recognize many com- 

 mon plant diseases by noticing 

 the effects produced on host 

 plants. These effects may be 

 regarded as symptoms of disease. 

 They are classified according to 

 the general appearance of the 

 injury, as follows: rot, blight, 

 wilt, mildew, leaf-spot, scab, canker, smut, and rust. 



Rot. The name itself suggests the nature of the injury 

 caused by this class of diseases. The fleshy parts of a plant 

 are most often affected, although the injury is found on other 

 parts of some plants. Examples : 



Bitter rot of the apple. It appears, at first, on the fruit 

 as small, round, rotten spots. Later the spot becomes dry 

 and dark colored. The spot increases in diameter, gradually 

 involving the entire fruit. The surface becomes wrinkled, 

 and, toward the center of the rotten area, small elevations 



Diagram of section of a leaf spot 

 of early blight of potato. 



A. Spores. 



B. Withered remains of cells 

 of leaf. Note how much this 

 portion of the leaf has shrunken. 



(Adapted from Rands: Wis- 

 consin Agricultural Experiment 

 Station.) 



