X45-10 MANUAL OF METHODS FOR PURE CULTURE STUDY 



means of a capillary tube and funnel. If an enzyme like pectinase 

 is being tested, thin sections of tissue need merely be immersed in a 

 few drops of the liquid. 



So many substances appearing in cultures influence plants in one 

 way or another that rigid controls are necessary in searching for the 

 products responsible for pathogenicity. Whenever feasible, an at- 

 tenuated culture of the same organism or a closely related non- 

 pathogenic culture is carried in a parallel series of trials. 



The methods of testing for plant "hormones" and "vitamines" are 

 being revised so rapidly that an active investigator should be con- 

 sulted for the latest procedure. 



ANTIBODY PRODUCTION 



Questions on the development of antibodies in plants following 

 inoculation or natural infection are discussed in a considerable litera- 

 ture reviewed by Chester (1933). A number of controversial points 

 are involved. 



The injection of plant bacteria into an experimental animal (see 

 Leaflet VIII) commonly results in the production of antibodies useful 

 for various investigations. Serological work with plant pathogens is 

 described by Link and his associates (1929, and earlier papers) and 

 by various other investigators. Methods of applying the precipitin 

 test to a study of certain viruses are given by Chester (1935). 



Cognate Considerations 



STRAIN variations 



When studies involving strain variations are made it is well to 

 consider Frobisher's (1933) comment, "Plating and fishing of colonies, 

 while generally useful, is not a sufficiently reliable method of purify- 

 ing cultures in work involving bacterial variations. It is sometimes 

 extremely difficult, if not impossible, to separate bacterial species by 

 this means. Single-cell methods are much more reliable and, it would 

 seem, furnish the only satisfactory means of solving our problems, 

 but even such procedures as are at our disposal require very expert 

 manipulation and may lead to error." The relative unreliability of 

 the poured-plate technic for such studies has been discussed by 

 Riker and Baldwin (1939). The need for cultures with a known 

 origin from a single cell has stimulated much work on methods for 

 securing them. Literature on this work has been reviewed by several 

 writers, e. g., Hildebrand (1938). Unfortunately, several recent 

 reports on bacterial variations have appeared in which the cultures 

 were purified merely by several successive dilution plates, and such 

 purified cultures were called "single-cell cultures." This misleading 

 use of a well-established phrase provides both the investigator and the 

 reader with a false sense of security. 



