Chapter III 



OBSERVATION AND DESCRIPTION 

 OF PENICILLIA 



A colony of Penicillium typically exliibits certain striking characteristics. 

 These include color and color changes; texture which may be velvety, 

 floccose, funiculose, or fasciculate or coremiform; and habit, which may be 

 restricted to broadly spreading and range from plane to deeply furrowed 

 or wrinkled. The substratum may or may not be discolored. Con- 

 spicuous drops of transpired fluid are characteristic of some species but 

 not of others. Odors may or may not be produced, and if present may be 

 fairly characteristic or just "moldy." Occasional records of changes in 

 the color and appearance of the colony, and its effect upon the substratum, 

 over a period of several weeks often provide useful information. 



After a preliminary examination with the naked eye, the hand lens, 

 and direct examination with the low powers of a compound microscope to 

 establish cultural characteristics, a microscopic mount enables one to 

 determine the details of structure and the pattern and dimensions of essen- 

 tial cells. Microscopic observations on Penicillium should begin within 

 a few days and follow the development of the colony throughout the grow- 

 ing period, usually comprising the first two weeks, and should include 

 examination of the submerged and aerial hyphae, the conidiophores, and 

 the arrangement of the cellular elements which comprise the conidial 

 apparatus. 



Eqtjipment 



A good hand lens or low power binocular is extremely useful for making 

 preliminary observations of colony characteristics. For closer examina- 

 tion, study of the fungus in petri dish cultures with the low powers of the 

 compound microscope is essential to an accurate description of the colony 

 itself. For making the necessary detailed studies of the penicillus apochro- 

 matic objectives are recommended, including if possible 16 mm., 8 mm., 

 4 mm., and either a 2 or 3 mm. oil immersion lens of 1.30 N.A. For use 

 with these lenses one should have lOX and 15X compensating oculars, one 

 of which is equipped with an eyepiece micrometer disk to afford constant 

 provision for measurement of cellular elements. 



Slide Mounts 



Preparations for microscopic examination present many difficulties 

 since the aerial parts of many Penicillia do not mix readily with water. 



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