62 Von SCHRENK: TEACHING OF VEGETABLE PATHOLOGY 
those factors which can be most readily handled, for it is after all, 
as has been said, the method of study that we are after, rather than 
along series of facts. This part of the work can of course be 
carried on hand-in-hand with that part first suggested, for it is 
not possible to separate cause and effect. 
Coming next to the influence of living organisms, a large field 
is opened with any number of possible lines of work. One of the 
first points to be demonstrated is that fungi or bacteria are the 
causes of disease. For this purpose it is well to select a fungus 
which grows readily and reproduces rapidly. There are a num- 
ber of these. This fall we found Zrysiphe graminis growing on 
wheat, a most interesting fungus to work with. I can perhaps 
make my meaning clearest by relating briefly what we did. A 
preliminary discussion brought out a number of questions which 
we desired to answer, such as : (1) Does this fungus produce the 
disease of wheat which it was found connected with, 2. ¢., will it 
make perfectly healthy plants diseased ? (2) How does it do $0; 
in other words, what is the relation of the fungus and the wheat 
leaf? (3) Willthe spores of the fungus produce the disease in other 
plants besides the wheat plant, for instance oats, rye, wheat, /4, 
corn, roses, etc. (4) Is there any connection between the ease 
with which this fungus attacks the wheat, and the condition of the 
plant to be infected? (5) What factors favor development of the 
fungus? Will the fungus grow on dead leaves? (6) How does 
the spore get from plant to plant? (7) What are the factors 
which determine germination of the spores ? 
Each student was instructed to find a method for answering 
these questions, and such others as arose, and as a result we had 
a series of experiments started, which were watched with the ut 
most interest. The questions dealt with broad subjects applica- 
ble to most other fungi or disease-causing factors. The results 
showed that the fungus does produce the disease, and thereby 
_ answered one of the most important questions, To the average 
mortal “ seein’ is believin’,”” and when a student actually sees him- 
self producing the disease in question, as he thinks, the impressio® 
- gained is that of the original investigator, and is apt to be remem 
bered. The results brought into discussion the problem of sus~ 
ceptibility, both of plant races and individuals ; it was found that 
