PLANT DISEASES 259 



EXERCISES 



EXERCISE I. Crown-gall. 



Material. Potted geranium plant with actively growing stems. 

 Secure specimens in the locality of crown-gall injury. (This will be 

 found on almost all of the deciduous fruit-trees, especially the peach.) 



Procedure. Note with regard to crown-gall the following points: 

 The general appearance of the diseased portion, its location with regard 

 to the surface of the ground, its effect on the living tissue of the plant, 

 the apparent depth of penetration into the interior of the plant, the 

 appearance of the center of the diseased portion as compared with its 

 outer edges and general appearance of the plant on which the crown-gall 

 is found. 



Transmit the disease from the affected plant to a healthy young 

 shoot of geranium in the following manner: Insert the point of a knife 

 blade into tissue affected with crown-gall and then insert the blade 

 into the young stem of the geranium. 



Each student should make this inoculation, some using the center of 

 the crown-gall tissue and others the outer edge. The geranium stems 

 thus inoculated should be watched carefully from day to day. The 

 effect of the inoculation will probably begin to appear within a month. 



EXERCISE II. Diseases affecting projects. 



Materials. Diseased portions of plants from students' projects. 



Procedure. Make a study of the diseased plants either in the 

 laboratory or in the field. Identify the disease by referring either to 

 Chapter XVII, to books of reference on plant diseases, to bulletins 

 published by the experiment stations, or in the event that the 

 identification is still uncertain, by direct correspondence with your 

 state experiment station. 



Write up a full account of the disease including the cause, nature of 

 injury, control, and all other material of interest. 



EXERCISE III. Study some of the common fungicides in the same 

 way as suggested for the study of insecticides in the exercises following 

 the chapter on "Insects." 



EXERCISE IV. Making various spray mixtures. 



Materials. Various materials for making spray mixtures, utensils 

 for making, and the like. 



Procedure. Make spray materials such as bordeaux solution and 

 lime sulfur. 



