Cryptogamic Botany and Plant Pathology. 409 



to tube No. 2, making the second dilution, and from No. 2 to 

 No. 3, making the third dilution. Experience enables one to 

 judge quite accurately in making the dilutions so that we esti- 

 mate the dilution sufficient to cause each gemi to lie separately 

 at different points in the liquid agar, at least in dilution No. 3. 



Each of. these dilutions was then poured into a Petrie dish,* 

 and allowed to cool in a thin layer over the bottom. No germs 

 could then be seen in the agar, since they are microscopic and 

 lie singly. The dishes were piled away for a few days. During 

 this time each germ grew and produced a colony which was 

 visible to the unaided eye. The plates or dish cultures were 

 now photographed natural size and the result is reproduced in 

 Plate I, In No. 3 it will be seen that nearly all of the colonies are 

 separate. The snowflake-like colonies are those of the desired 

 fungus. The small, compact, circular ones are those of bacteria. 

 One large compact colony is that of a common fungus. 



In Nos. 2 and 1 the fungus colonies are crowded, and have not 

 made such good growth. The colonies of bacteria are more 

 numerous also, and it would be very difficult to obtain a pure 

 culture of the fungus in either of those dilutions. If the dilu- 

 tions were not numbered it would be an easy thing to determine 

 their number from the size and number of the colonies. The 

 very large compact colony in No. 2 is that of a motile bacterium. 



Pure cultures of the anthracnose. — Pure culture of the fungus 

 could now be started by transplanting with a flamed platinum] 

 needle portions of the fungus colonies from No. 3 into a culture 

 tube of nutrient agar. The photograph was taken after these 

 transplantings were made which accounts for the broken appear- 

 ance of some of the colonies. 



From the point of inoculation in the culture tube, where the 

 transplanting was made, the fungus threads gi'ow out through 

 the upper surface of the agar radiating in all directions. In a 

 few days minute black bodies appear seated here and there upon 



*A Petrie dish is composed of two shallow glass vessels, one about three 

 inches in diaiiieter which serves as the bottom, the other of a little greater 

 diameter, which is inverted over the first one for a cover. 



52 



