48 A MANUAL OF THE PENICILLIA 



been variously termed branches, basidia, secondary sterigmata and finally 

 metulae by Westling (1911). 



The metulae usually follow closely the diameter of the conidiophore 

 and whatever branches it may produce; less commonly they may be con- 

 spicuously smaller in diameter. They are often somewhat enlarged at 

 the tip. In length they may vary quite appreciably or be more or less 

 constant depending upon the species and strain. They generally average 

 a little longer than the sterigmata and their arrangement is fairly charac- 

 teristic of the species. Variations in shape are usually such as may be 

 attributed to the effect of crowding several elongated cells into a compact 

 verticil upon the apex of the fertile branch. Whenever the walls of the 

 conidiophore are smooth, those of the metulae are also consistently smooth. 

 When the walls of the conidiphore are pitted or rough, the walls of the 

 metulae may or may not be similarly roughened. 



Branches 



In the larger penicilli produced by some of the Asymmetrica, where 

 more than one verticil of metulae is developed, the cells, other than the 

 main axis which bear such metulae, are referred to as branches (fig. 7B). 

 In certain species the penicillus is usually typified by a single branch; in 

 others one or more branches may be produced. However, in many forms, 

 including the members of the Biverticillata-Symmetrica, branches are 

 seldom if ever produced and the metulae are borne only as a terminal 

 verticil on the main conidiophore axis. Biourge referred to branches 

 as rami. 



CONIDIA 



Every conidium arises theoretically as a cylindrical body cut from the 

 tube-like tip of a fertile cell, or sterigma. Changes from the cylindrical 

 form maj^ begin well before the separation of the cell has become evident 

 by the formation of a definite cross-wall, or this may be delayed. In a 

 few forms, such as Penicilliimi digitatum Saccardo (fig. 12A) and P. itali- 

 cum Wehmer, the cylindrical shape of the conidia persists for a consider- 

 able time before it gradually becomes transformed to elliptical. In still 

 other species, such as P. bacillosporum Swift, the conidia retain a cylindri- 

 cal shape indefinitely (fig. 153). In the Biverticillata-Symmetrica the 

 conidium typically first appears as a long cylindrical segment of small 

 diameter, and tends to become fusiform by an increase in diameter at its 

 center. In other species the length of the original segment is only a little 

 greater than its diameter, hence the conidium quickly becomes globose 

 or subglobose. In still other species it starts out as an elliptical segment 

 and reaches a globose form by a general and continued swelling of the en- 



