104 FUNGOUS DISEASES OF PLANTS 



Owing to the simple forms of these organisms, a thorough 

 knowledge of the morphology of a species would not alone 

 suffice, even roughly, to differentiate the numberless more or 

 less similar species. Fortunately, the development of pure-culture 

 methods has made possible a variety of tests, or points of com- 

 parison. Growth characteristics of colonies, the reactions and 

 products on numerous culture media, the thermal, photal, patho- 

 logical, and other relations of the germ — in short, all physiolog- 

 ical properties — must be studied and tabulated in order to make 

 accurate and trustworthy comparisons. 



Recently a descriptive chart has been prepared for the Society 

 of American Bacteriologists * which indicates concisely, yet com- 

 pletely, the characters which should be carefully studied and tabu- 

 lated in the case of any organism before it may be said that the 

 organism may be fully and properly described. This chart should 

 be in the hands of every student and would serve as a score card. 

 In short, the description covers general morphology, cultural fea- 

 tures, certain physical and biochemical characteristics, and patho- 

 genic relations. Under morphology, size, form, and adherence of 

 the vegetative cells are noted. The nature of the movement, the 

 type of endospores, flagella, capsules, zooglcea, involution forms, 

 and staining reactions should be followed. The cultural features 

 include a complete discussion of agar, streak and stab cultures, and 

 also cultures on potato, blood serum, gelatin, beef broth, milk or 

 litmus milk, starch jelly, silicate jelly, a special study of the colo- 

 nies on agar and gelatin, and the special growth reactions upon 

 synthesized nutrient solutions. 



The physico-chemical features are concerned with the produc- 

 tion of gases, acids, alkalis, alcohol, ferments, etc. ; the reduction 

 of nitrates, or the presence of nitrites or nitrates in the culture ; 

 indol-production, resistance toward acids, alkalis and other toxic 

 agents ; vitality ; and temperature relations, particularly the thermal 

 death point, the maximum, minimum, and optimum for growth. 



In the case of the pathogenic organisms, a complete study of 

 infection, the relation of the organism to the legions produced, and 

 special reaction of hosts and parasite should be considered. 



1 This chart was prepared by F. D. Chester, F. T. Gorham, and Erwin F. Smith, 

 and was indorsed by the Society at its annual meeting, December 31, 1907. 



