1893.] MICROSCOPICAL JOURNAL. 123 



the tliird ililution. Experience enables one to judg'e quite accu- 

 rately in making the dilutions so that we estimate the dilution 

 sufficient to cause each germ to lie separately at dillerent 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 visi- 

 ble to the unaided eye. The plates or dish cultures were now 

 photographed naturalsize and the result is produced in the frontis- 

 piece. In Np. 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. 3 and i the fungus colonies are crowded, and have not 

 made such good growth. The colonies of bacteria are more 

 numerous also, and it would be ver}' ditficult to obtain a pure cul- 

 ture of the fungus in either of those dilutions. If the dilutions 

 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 cultures of the 

 fungus could now be started by transplanting with a flamed plati- 

 num needle portions of the fungus colonies from No. 3 into a cul- 

 ture-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 grow out through the 

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

 days ininute black bodies appear seated here and there upon the 

 mycelium. These resemble the stroma at the base of the pus- 

 tules on the stem, but in the artificial cultures do not seem to be 

 especially concerned in the production or basidia and spores, 

 since but a few are developed in connection with them. 



Numerous basidia and spores are produced, however, all along 

 the threads, and a mass of them at the point of inoculation. In 

 a few days more many fungus threads arise above the agar and 

 produce a fluffy white growth upon the surface, nearly obscuring 

 the black points. 



No pigment was noticeable in these cultures. New cultures 

 were then started by transplanting portions of agar the size of a 

 small pea with a mat of mycelium and spores to fresh culture- 

 tubes. In the fresh agar the growth took place in the same man- 

 ner as in the first tubes, but upon the surface of the transplanted 

 poi'iions a faint pink pigment appeai^ed, 



* A petrie di^h is composed of two shallow glass vessels, one about three inches in diame- 

 ter, which serves as the bottom ; the other of a little greater diameter, which is inverted over the 

 first one for a cover. 



