METHODS OF INVESTIGATING PLANT DISEASES. 173: 



themselves for this important work, and much is being accom- 

 phshed every year that has not only a direct scientific value but 

 means dollars and cents in the pockets of horticulturists and 

 agriculturists. 



We must recognize then this line of work as preeminently 

 the province of plant pathology, altho in the broadest applica- 

 tion of the subject it includes all inorganic, and insect troubles 

 as well. It is concerning some of the methods used in investi- 

 gating diseases due to parasitic organisms that I wish to speak 

 to you this afternoon. It is not my purpose to enter into de- 

 tail in regard to the different methods that may be used by the 

 pathologist, for many are decidedly complicated, but to give 

 you rather a general idea of the character of the work possible. 



There are two classes of plants that are important as the 

 causal agents of the diseases of our cultivated plants: the bac- 

 teria and the fungi. I need have no hesitation in using the 

 word bacteria, since the importance of these simplest of all or- 

 ganisms in many lines of human activity has made the name a 

 household word. The bacteria are the smallest living organisms 

 but they are most powerful. Probably not many of you have 

 ever seen bacteria, altho you have seen their devastations. I 

 have here the bacterium of "fire-blight," that deadly disease of 

 apple and pear trees that is familiar to all of you. What you 

 see is not one organism but millions. There are enough here 

 in this tube to kill every apple tree in the state of Nebraska. 

 Only a comparison can give you an idea of their minuteness. If 

 one hundred were placed side by side, their total thickness 

 would not equal the thickness of a single sheet of my manu- 

 script paper. Let us put it in another way: I should have to 

 increase the mass of a blight germ 22,000 times to get a body 

 as large as a spore of the carnation rust, yet that is almost be- 

 yond the limits of vision; again, I should have to multiply this 

 by 350,000 to get a body as large as a number seven shot. If 

 you should conceive of a number seven shot as a hollow sphere, 

 there would be room and to spare inside it for something like 

 8,000,000,000 of the blight bacteria. Such statements are of 

 value only as serving to give you an idea of the minuteness of 

 these organisms. Is it strange then considering their minute- 

 ness that the elaboration of the methods for studying and hand- 



