144 MYCOLOGY 



Thielavia. The perithecia are never subterranean. They are usually 

 small, spheric, usually closed, and their walls are made up of pseudo- 

 parenchymatous hyphae. They rarely open by a pore, more usually 

 they break up at maturity to allow the escape of the ascospores. The 

 inclosed asci are spheric to pear-shaped and two- to eight-spored. 



The moulds of the genus Aspergillus (Figs. 49 and 50) are usually 

 saprophytic, and are found upon decaying vegetables, moldy corn and 

 other cereads. After the conidiospores are formed, the color of the 

 mould develops and various shades of green, white, blackish-brown, 

 brownish-yellow, brown and reddish are found in the different species 

 of the genus. The.recognition of this genus is made easy by the shape 

 of the conidiophores, which are elongated unicellular (unseptate) and 

 terminate in a globular swelling, the top of which is covered with a large 

 number of closely set stalks, or sterigmata, of variable length and shape 

 on which the conidiospores develop. In the related genus Sterigmato- 

 cystis, the sterigmata are branched (Fig. 51). The conidiospores are 

 spheric, or ellipsoidal, always unicellular with smooth or granular 

 walls, and are formed in long chains (concatenation) from each sterigma 

 imparting the characteristic color to the whole growth. The perithecia 

 are fragile spheres with thin walls which may be yellow (A. herbari- 

 orum) dark red {A. pseudo-clavatus), or even black {A. fumigatus) 

 in color. The perithecia and asci are unknown in many of the species, 

 so that the classification of the species cannot be based on the characters 

 of that organ and of the ascospores. Only about six to ten species are 

 known to have perithecia out of a possible total number of 1 20 species 

 included in the genus. This number will probably be considerably 

 reduced when these moulds are better known. The accompanying 

 figures show some of the specific differences of the conidiophores and 

 conidiospore production. The common green mould, Aspergillus 

 herbariorum (= Aspergillus glaucus, Eurotium Aspergillus glaucus) 

 grows on many substances such as dried plants in the herbarium, 

 (hence its specific name), on old black bread (pumpernickel), on jellies, 

 on jams, on old leather, on herring pickle and other objects of domestic 

 use. At first the mycelium is white and as the young conidiospores begin 

 to form it turns to a pale green, later becoming a dirty grayish green, 

 while the feeding hyphae change color to a pale yellow and finally a 

 brown color by the deposit of pigment granules. The globular part of 

 the conidiophore is 60^ across and crowded with simple sterigmata 



