Oct. 2, I916 
Aspergillus niger Group 
7 
Heads. —Conidial heads vary exceedingly in size; the common forms 
show simultaneously mature heads varying from 100 to 400/A in diameter. 
This maximum becomes 1,000/1 or more in the gigantic forms. The 
chains of conidia at first radiate uniformly, but as they lengthen they 
adhere into black masses or columns which separate more and more as size 
increases. 
VesiceE. —The vesicle or enlarged apex of the stalk varies commonly 
from 20 to 50 /a, but occasionally reaches 80 to ioo/a; it is continuous with 
the lumen of the stalk, thick-walled, and with walls and often contents 
yellow to brown in age. 
Sterigmata. —The vesicle is fertile over its whole surface and bears 
sterigmata usually in two series. Examination of young or growing 
colonies commonly shows individual heads producing conidia upon 
sterigmata of the first series, other heads with both simple and branched 
sterigmata, and heads with well-differentiated primary sterigmata, each 
bearing its quota of three to several secondary sterigmata. Here, as 
elsewhere, the variations of measurement in the same colony destroy all 
faith in such figures as an exact means of separating forms. The classic 
descriptions of A . niger as summarized by Wehmer 1 give the primary 
sterigmata as 26 by 4 to 5 /a, the secondary as 8 by 3/A. The secondary 
sterigmata vary perhaps within limits of 6 to io/a by 2 to 4 /a in the whole 
series, with 8 by 3/4 as a fair average figure. The variation in primary 
sterigmata makes a length of 26/A an occasional average for sleeted heads 
only. Examination of many heads in some strains gives lengths of primary 
sterigmata averaging between 12 and 20/A with an occasional longer cluster 
and frequently much of this variation occurs within the individual head. 
In another group the maximum length lies between 20 and 30/A. Again, 
in a few strains, lengths of 40 to 6o/a are seen, while two of this series in 
their largest heads show primary sterigmata up to 120/t in length, as 
given by Bainier 2 for S. carbonaria. 
Conidia. —The formation of conidia in the A. niger series follows the 
process described by Thom 3 for Penicillium spp. This probably agrees 
with the process designated as endogenous by Bainier and Sartory 4 in 
that each conidium is first cut off from the conidial tube of the sterigma, 
then rounds itself up after secreting for itself a new wall, while the original 
cell wall is frequently distinguishable between the ripe conidia as a con¬ 
nective. Ripe conidia are subglobose, with, in most strains, a variation 
in the same culture of about i/a in diameter; some run from 2.5 to 3.6/A, 
1 Wehmer, Carl. Die Pilzgattung Aspergillus in morphologischer, physiologischer imd systematischer 
Beziehung unter besonderer Beriicksichtigung der mitteleuropaeischen Species. V. Systematik. C. 
Schwarzbraune Arten. In Mem. Soc. Phys. et Hist. Nat. Geneve, t. 33, pt. 2, no. 4, p. 103-107. 1901. 
2 Bainier, Georges. Sterigmatocystis et nematogonum. In Bui. Soc. Bot. France, t. 27 (s. 2, t. 2), p. 
29^30. 1880. 
8 Thom, Charles. Conidium production in Penicillium. In Mycologia, v. 6 , no. 4, p. 211-215, 1 fig. 
1914- 
4 Bainier, Georges, and Sartory, Auguste. Etude d’un Aspergillus pathogene (Aspergillus fumigatoides 
n. sp.). In Bui. Soc. Mycol. France, t. 25, fasc. 2, p. 112. 1909. 
