USE OF THE MANUAL 113 



lose if conidial structures arise largely, or in part, from ropes or bundles of 

 aerial hyphae (fig. 4A) ; colonies are regarded as fasciculate if conidiophores 

 are aggregated into bundles, fascicles, or coremia to produce a tufted, fas- 

 ciculate, or coremiform appearance (fig. 4B). 



In the Asymmetrica these growth types are especially pronounced and 

 major sub-sections are centered around them. In the Monoverticillata 

 and in the Biverticillata-Symmetrica they are used as a basis for the sepa- 

 ration of series. The above characteristics are of great usefulness in the 

 arbitrary system of classification which is of necessity employed in the genus 

 Penicillium. They are not, however, fixed either in character or continuity. 

 For example, strains of some species which are characteristically velvety 

 when freshly isolated, may, through progressive variation in laboratory 

 culture, develop into forms that are essentially floccose or funiculose. On 

 the other hand, strains which are at first strongly fasciculate may lose their 

 capacity to produce conidiophores in bundles or fascicles and hence assume 

 a velvety appearance. Other shifts in colony character may likewise occur. 

 In the presence of such changes in pattern of growth the use of colony tex- 

 ture must be tempered by the best judgment of the worker and correct 

 assignment of the strain or species must depend upon a careful analysis of 

 the total cultural and morphological characteristics of the particular 

 organism. 



Additional bases of separation are useful within the different sub-sections 

 and series. These may hinge upon the pigmentation of conidial areas and 

 colony reverse; upon the rate of growth on common laboratory media; or 

 upon the pattern assumed by mature conidial chains, i.e., whether they 

 remain adherent into columns, become widely divergent, or irregularly 

 tangled. Again separation may depend upon the detailed structure of the 

 penicillus, the pattern or character of the sterigmata, the form and markings 

 of the conidiophores. or the shape and dimensions of the conidia. 



Series 



Individual strains, or aggregates of strains, in Penicillium are not gener- 

 ally set apart from all other strains sharply enough to guarantee either 

 absolute individuality or complete duplication of forms already encoun- 

 tered. Usually, however, they seem to fall into some general series pat- 

 tern. When more and more strains are examined, this series pattern tends 

 to become more real, whereas the individuality of specific strains becomes 

 less apparent. Thus, if only a few strains in a limited group, or series, are 

 examined it is often easily possible to recognize several species; if, however, 

 large numbers of strains are isolated and carefully compared, the definite- 

 ness of estabfished species boimdaries gradually recedes. Finally, it may 

 prove difficult to establish any clear lines of separation, and species, if 



