DETERMINATION OF MORPHOLOGY 67 



The first step in identifying a mold is to determine whether it be- 

 longs to the Phycomycetes or the Ascomycetes (or Fungi Imperfecti). 

 In general, though there are exceptions, this may be readily done by 

 a rather superficial examination. With those species which belong to 

 the Fungi Imperfecti the plant mass is usually relatively compact, 

 the aerial filaments of mycelium are relatively short, and the sur- 

 face is thickly covered with spores which are frequently brightly 

 colored. The surface may be compared to the nap of velvet. In 

 the phycomycetous molds the mycelium is coarser and looser in tex- 

 ture, the aerial hyphae are longer, and the sporangia are less numer- 

 ous. The spore heads and frequently the aerial mycelium are usually 

 dark colored, brown, gray or black. The whole plant mass has a 

 texture comparable to cotton wool. 



Molds take up considerable water from the medium and give off 

 considerable into the air, which may condense in droplets on the 

 surface of the plant. Large amounts of this transpiration (or gutta- 

 tion) water are characteristic of certain species. The droplets are 

 frequently colored by pigments excreted by the mold. Beginners are 

 frequently apt to jnistake these droplets of moisture on the mycelium, 

 especially if it is colored, for spores or other structures. 



The general characters of the aerial mycelium and the spore heads 

 may be determined by examining the growth with a magnifying glass 

 or the low-power lens of the microscope from above, after removing 

 the cover of the dish. For this purpose a binocular dissecting micro- 

 scope is ideal. 



After examining the upper surface of a Petri plate culture, one 

 should reverse the plate and note the under surface of the colony. 

 Frequently very characteristic colors are produced in the submersed 

 mycelium or in the medium itself. These will vary markedly with 

 the medium. Some of the pigments act as indicators, being perhaps 

 yellow on one side of neutrality and red on the other. Occasionally 

 one may find pigment only at the spot where two different molds 

 come together. Particularly one should note if the submersed my- 

 cehum is light or dark in color. This is important as a primary 

 separation of molds belonging to the Fungi Imperfecti. 



In the examination and culture of sputum, species of Candida are 

 frequently found. The most important of these, Candida albicans, 

 can be readily identified in most cases by its appearance on corn 

 meal agar in a plate culture. The agar is inoculated by placing the 

 inoculum in several parallel streaks across the plate; a stiff needle 

 is used so that some of the inoculum is below the agar surface. After 

 4 or 5 days of incubation at 20° to 25° C. the species produces char- 



