614 



MEDICAL MYCOLOGY 



diagnostic characters (Fig. 93). The phialide narrows at the apex into a 

 thin-walled tube from which all conidia arise. The tube lengthens, mitosis 

 is followed by the formation of a secondary wall around the newly formed 

 conidium within the original wall of the tube. This is followed by rapid 

 growth of the conidium which assumes the size and shape characteristic for 

 the species. The original conidial wall may remain visible as a disjunctor 

 or bridge between the conidia in the chain and may be further emphasized by 

 the deposit of granules, tubercles, or bars of color between the outer or pri- 

 mary wall and the inner, secondary, true conidial wall. In some species the 

 two walls are indistinguishable, although the inner wall may be much thick- 

 ened, pitted, or grooved. 



This method is in sharp contrast with that in Horniodendrum and Clado- 

 sporiiim Avhere the conidia bud out from the tip of a more or less specialized 

 erect or prostrate, branch and continue to bud from the apex and from various 

 nodes of the branch, producing a dendroid mass with the newer cells at the 

 tips. In the Aspergillaceae, the youngest conidium in the unbranched chain 

 is always the one nearest the phialide. 



Fig. 93. — Types of phialides. A, acute type; B, acuminate type; C, Paecilomyces type 

 with its long tube turned sharply away from the axis of the cell ; D-I, beaked types ; J, 

 Soopulariopsis type. (After Thorn 1930.) 



Dangeard reports that the conidia of the Aspergillus glaucus group are mul- 

 tinucleate, while those of all the other groups studied by him are uninucleate. 



In Penicillium (Thom 1930), the conidiophore lacks a differentiated foot 

 cell, and the conidial bearing organs are borne on a complex system of branches 

 known as a penicillus instead of upon a vesicle (Fig. 94). If each terminal 

 branchlet with its cluster of phialides and conidial chains seems to stand out 

 separately, the penicillus is called monoverticillate. It may be borne upon 

 an irregular system of branches at various levels along a common fertile 

 hypha, or on one of several diverging branchlets from the tip of the main 

 axis. If branching occurs at two levels, either asymmetrically or symmetri- 

 cally about the center, it is called biverticillate. The asymmetric group does 

 not seem to be homogeneous. 



The terminal branches of the penicillus are usually very uniform and 

 differentiated from the other branches. They are generally called metulae 

 and bear a verticil of phialides on their tips. The shape of the phialide is 



