16 PAEASITES BELONGING TO THE GENUS GLOMEKELLA. 



cient power to distinguish and identify them clearly through the bot- 

 tom of the dish. The location of the single spores is then indicated 

 by a small circle of red ink on the bottom of the Petri dish. The cul- 

 ture medium in the dish should be very shallow, so that the range of 

 the objective will reach through the full depth of the medium and per- 

 mit the detection of spores lying at different levels. Some practice 

 in getting the proper dilution of the spores in the medium is required. 

 When the spores are too numerous in the plates it is frequently diffi- 

 cult to find one sufficiently isolated to be readily removed without 

 the possibility of others being transferred with it. When the spores 

 are too few, however, much time is required in searching over the plate 

 to locate them. 



Spores have also been isolated by the method described by Kauff- 

 mann (50). This method consists in sprinkling sterile water contain- 

 ing the spores on the surface of the agar after it has been poured in a 

 Petri dish and cooled. When the medium has solidified, the spores 

 are located with the microscope by examining the surface of the agar 

 with the cover of the dish removed. This method has the advantage 

 of insuring the distribution of the spores in practically one plane — i. e., 

 on the surface of the medium — and permitting the use of a higher 

 power objective than could be used when searching through the bot- 

 tom of the dish. It has the disadvantage, however, of necessitating 

 the removal of the cover during the search for the spores and thus 

 greatly increasing the liability of contaminating the culture; but this 

 tendency can be largely overcome by making the examination in a 

 thoroughly protected culture room. With thin dishes and a thin la} r er 

 of culture medium, spores not less than eight microns long can be 

 located very satisfactorily by the first method. With smaller spores 

 requiring high power for identification, the second method is prefer- 

 able. As soon as the spores have germinated, which usually requires 

 8 to 16 hours, they are carefully transferred by means of flattened 

 sterile needles to tubes of the same medium. If the germinating 

 spore is transplanted near the upper margin of the agar and close to 

 the wall of the tube, it msij be usually located with the microscope 

 and its actual transfer to the tube verified. 



Pure lines, races, or strains can be isolated in this manner, then 

 propagated indefinitely by transfer to subcultures or by the poured- 

 plate method, thus making it possible to study the behavior of the 

 organism in relation to various factors of nutriment and environment 

 through as many generations as is desired. 



STUDIES OF GLOMERELLA FROM DIFFERENT HOSTS. 



The following records give the results of the writers' studies of 

 Glomerella, Gloeosporium, and Colletotrichum from various host 

 plants, describing their behavior on leaves, stems, and fruits in 



252 



