CULTIVATION AND PRESERVATION OF PENICILLIA 71 



primary tubes can be easily destroyed. If, on the other hand, such pri- 

 mary tubes are not made, subsequent studies may be seriously interfered 

 with by contamination or accidents in handling. A half dozen tube trans- 

 fers afford a measure of insurance out of all proportion to the time required 

 for their preparation. Such tube cultures, however, cannot be recom- 

 mended for observation: (1) the colony area is generally too small and too 

 confined for the development of wholly characteristic cultural patterns; 

 (2) the culture cannot be viewed directly with the low powers of the com- 

 pound microscope; and (3) portions of the growing colony cannot be care- 

 fully selected and easily removed for the preparation of suitable micro- 

 scopic mounts. 



Plate Cultures 



The success of taxonomic studies in the genus PenicilUum hinges upon 

 the cultivation of these molds in petri dishes where cultural and micro- 

 scopical developments can be followed simultaneously throughout the 

 growing period. Different types of plate cultures have special applica- 

 tions : 



Spot Cultures: The type of culture most commonly employed is based 

 upon the spot inoculation of agar plates with masses of conidia or bits of 

 mycelium from a selected area in the parent culture. Such transfers can 

 be made by means of a conventional wire needle or loop. For most work 

 it is not necessary to have in the developing culture a particular number 

 of colonies, although these should not be so numerous as to preclude the 

 development of normal colony patterns. Where it is desired to establish 

 a specific number of colonies in particular positions within the culture 

 plate, it is advisable to suspend the conidia in water, or better still in 

 melted agar, at about 45°C. and then transfer small amounts of the gelled 

 spore suspension to the fresh culture. Single colonies are desirable for 

 some types of observation and these can be established in the same manner. 

 For most types of work, however, cultures showing two or more colonies 

 are more useful. In such cultures one can study the mature growth and 

 fruiting habits of the mold best in the area where the colonies approach 

 one another, whereas their habits of vegetative growth can, at the same 

 time, be studied at the opposite side of the colony where growth remains 

 imrestricted. For our work we have found plates inoculated with three 

 colonies to be generally satisfactory and to offer a degree of uniformity, 

 useful for comparative purposes, which cannot be attained where either a 

 single or an indefinite number of colonies develop. 



Selection of the inoculum for this or other types of cultures to be subse- 

 quently considered, can best be accomplished with the aid of a lOX pocket 

 magnifier or a wide field binocular microscope. Using the latter instru- 



