174 NEBRASKA STATE HORTICULTURAL SOCIETY. 



ling these and many similar organisms has been a slow and la- 

 borious process. It is not however an exaggeration to say that 

 at present the plant pathologist can transplant a single germ 

 as easily as you can transplant a green house plant. 



The number of bacteria that cause disease in plants is not 

 great, but new diseases are constantly being discovered. Only 

 recently a bacterial trouble of calla-lily bulbs has been added to 

 our list. Since Burrill first discovered the blight bacterium in 

 1880 something like thirty different bacterial troubles have been 

 recorded. Of this total number probably not over half a dozen 

 are prevalent in Nebraska. 



The other group of plants, the fungi, many of which are fami- 

 liar to you in the mildews, blights, smuts, rusts, and leaf spots, 

 are of even more importance than the bacteria as the cause of - 

 diseases in plants. The total number of species of fungi maybe 

 estimated at something like 40,000. Of the total number per- 

 haps 8,000 are found in North America, and of these not more 

 than one-fourth are the cause of disease, yet this is a vast and 

 powerful army. Only a fraction of the diseases are prevalent 

 in our own state, but new diseases make their appearance from 

 time to time, and as sporadic cases or general epidemics call for 

 investigation, in field and laboratory. 



Many of the fungi are but little larger than the bacteria and 

 here again the investigator encounters difficulties that are only 

 being overcome by use of modern laboratory methods. There is 

 hardly a cultivated i^lant that is exempt from attacks, so many 

 are the hosts of numerous parasites. The apple for example is 

 attacked by something like sixty different species. I have here 

 several examples of these injurious parasites: the brown rot of 

 apple, cherry, plum, peach: the green mould, which is one of 

 the most important apple rotting organisms; and a common foe 

 of green-house or hot-house plants (Botrytis). These few illus- 

 trations will serve to show you what some of these organisms 

 look like in a state of captivity. 



The advances made in the study of plant diseases have been 

 slow until recent years for at least two reasons. First, in the 

 earlier development of the subject, the microscope was the 

 principal instrument of research. Of course the microscope 



