ASPERGILLUS 



99 



chains of conidia are borne over the whole vesicle and the spore 

 head is thus spherical ; in other species the sterigmata are found only 

 on the upper part of the vesicle and the sterigmata and chains may 

 spread out, in cross section like a fan, or all sterigmata may point 

 upward, and the head appears like a long 

 cylinder. 



In some species of Aspergillus, ascospores 

 are found, i.e., these molds are perfect fungi 

 and should be included in the Ascomycetes. 

 A strict interpretation of International 

 Rules would seem to make it obligatory 

 to transfer these species to the genus 

 Eurotium as many authors have done. 

 However, the fact that the whole group of 

 Aspergilli appear to be so obviously 

 homogenous, falling naturally into one 

 genus, together with the fact that so many 

 species do not form ascospores at all, 

 makes it preferable for the sake of con- 

 venience, if for no other reason, to follow 

 the lead of most of the workers who have 

 actually worked extensively with these 

 molds, and put all species in the genus 

 Aspergillus. The ascospores are all more 

 or less of the same basic pattern. The 

 "thickening of the cell-wall of the asco- 

 spore develops in the form of two sym- 

 metrical valves suggesting the arrange- 

 ment found in the shell of a bivalve 

 mollusk {Venus mercenaria) . The ripe 



ascospore is commonly shaped as a double convex lens with the 

 valves more or less closely in contact at the edges. A series of 

 variations upon this basic pattern occur and characterize particular 

 species." (Thom and Raper.) The ascospores are borne eight per 

 ascus in round to oval asci and the asci are scattered throughout 

 the perithecium in an irregular arrangement. 



The perithecia are often very abundant and they may determine 

 the color of the colony. In most species of Aspergillus the perithecia 

 are formed on ordinary media with sugar, either regularly and abun- 

 dantly or not at all. They are found throughout the aerial mycelial 

 growth. They are formed after homothallic conjugation. By crush- 

 ing the perithecia under a cover slip, one can usually demonstrate the 



Fig. 46. A conidiophore 

 of Aspergillus nidulans, 

 showing the foot cell, 

 stalk, vesicle, and chains 

 of conidia. Photomicro- 

 graph from a slide culture. 



