Characteristics of Fungi on Culture 257 



the growth; culture mediums containing dextrose or other nutrient sub- 

 stances support more vigorous colonies than starvation mediums without 

 these substances. 



5. The luxuriance ol growth is characteristic. Fungi differ in their capac 



ity to develop. One Fungus covers the entire surface of an agar slant within 

 two weeks; another fungus, such as A. schoenleinii, never covers more than 

 a small portion. YVeidman pointed out that there is a difference between 

 volume and luxuriance of growth, although the two are usually seen to- 

 gether. The same factors which influence the rate of growth also affect the 

 character of the colony. 



6. Surface 1 configuration aids diagnosis. The gross topographic char- 

 acteristics of colonies (probably due in part to inequalities in growth) vary 

 considerably. A colony may be Hat, rounded, fissured, cerebri form, urn- 

 bilicated, folded or concentrically ringed. More than one feature may be 

 present in the same colony. Changes in the composition of the medium may 

 affect the gross appearance of a colony. The depth of the agar influences 

 the appearance; this can be seen when a growth is present along the 

 entire length of an agar slant where there is considerable variation in 

 thickness. In general, the depth of agar required for mycologic specimens 

 is greater than that used ordinarily in bacteriologic technic. 



7. The margin of the colony may be sharply defined or may lade into 

 the medium. 



8. The texture of colonial growths of fungi varies a good deal. One ob- 

 serves a downy or filamentous growth when the vegetative aerial mycelium 

 predominates and is loosely arranged. If the mycelium is closer together, 

 the growth appears compact or velvety. A granular surface is due to the 

 presence of spores. A pasty surface denotes a yeastlike micro-organism, 

 and a waxy appearance is characteristic of A. schoenleini. 



9. The color both of the colony and of the medium is occasionally an 

 important feature. A violet hue of the colony of T. violaeeum is character- 

 istic. The typical port-wane stain of T. purpureum rarely appears in the 

 growth until after two or three weeks. Pigment usually appears first on the 

 under side of the colony. A brownish discoloration of the medium is ob- 

 served with many different fungi. Many fungi lose their colors after re- 

 peated subcultures. The character of the culture medium is important, 

 since some mediums (like potato) will demonstrate pigment that ordinarily 

 is not present. 



10. Submergence of the colony is seen in cultural growths of A. schoen- 

 leini and of several other fungi. Splitting of the medium (due to the wedge 

 of growth) is not uncommon in old, compact growths. 



The same strain of fungus is subject to a range ot variation in cultural 



