OBSERVATION AND DESCRIPTION OF PENICILLIA 51 



in which the conidia seemed to be foi-med within the sterigma tube as de- 

 scribed_by Guegen and as illustrated by Scaramella (1928) for Penidllium 

 digitatum. WTiereas the latter type of development may occur occa- 

 sionally in other series of Penidllium, particularly in old sterigmata, it is 

 most readily observable in strains of P. digitatum and in a strain regarded 

 by us as representing P. tardum Thom (fig. 12C) but received from Pro- 

 fessor Westerdijk as P. scorteum of Takeda, Suematsu, and Nakazawa 

 (see p. 653). The latter type of conidium formation is strongly suggestive 

 of the dematiaceous genus Cadophora. 



Connectives 



Once formed, the conidium reaches a characteristic shape and pattern 

 by enlarging and laying down a new wall wthin the primary wall, which 

 is continuous vdih that of the parent cell. The presence of the vest- 

 igial cell wall as a connective (fig. 12): between conidia within the chain is 

 common in some species and occasionally seen in others. This ap- 

 pearance has been referred to as a bridge, disjunctor, or connective by 

 various authors, and considerable importance has often been ascribed 

 to it. Thom, 1914a, showed it to be merely incidental to the formation of 

 the thickened cell wall of the conidium itself, leaving occasional gaps be- 

 tween the new wall and the old when the rounding conidia drew apart in 

 their development. The view that the connective represents an abortive 

 cell was effectively disposed of by Thom in 1914a. 



Size of Conidia 



The measurements of conidia form a part of every species descrip- 

 tion. These are expressed in microns (n), either as the diameter or 

 range in measurement for globose series, or as the long axis by the short 

 axis for elliptical or subglobose cells. In many of our strains, some of 

 which have been kept in continuous culture for more than 40 years, meas- 

 urements show a fairly consistent range of variation, hence afford a rea- 

 sonable criterion for use in strain or species identification. In the 

 ordinary microscopic field there are hundreds of conidia in which the range 

 of measurements can be carefully observed and recorded together with the 

 limits most frequently seen. Results may be expressed in various ways, 

 preferably as a fairly narrow range of measurement covering the majority 

 of cells, but often supplemented by additional figures to show the more 

 complete variation encountered, especially if this is marked. Few lots 

 of conidia fail to show a considerable range in diameter. Figures to the 

 tenth of a micron, therefore, mean little unless the range of variation is 

 indicated or implied. A series of figures clearly setting forth the range of 

 dimensions encountered is worth immeasurably more than a precise value 



