THALLOPHYTES 
results in a filament of four cells, each of which gives rise to a slender 
branch bearing a spore (fig. 194). This saprophytic filament has been 
called the promycelium, and its spores sporidia; 
but it represents a four-celled basidium bearing 
basidiospores, and is the structure that determines 
the position of rusts among Basidiomycetes. 
Aecidium. The basidiospores that fall upon 
young barberry leaves germinate, and an extensive 
mycelium is developed among the tissues of the 
new host. This mycelium develops very evident 
structures of two kinds. Opening usually upon 
the upper surface of the leaf, small, flask-shaped 
organs appear, known as spermogonia, within which 
there arise slender filaments that form by succes- 
sive abstractions numerous very small cells, the 
spermatia (fig. 195). The names spermogonium 
and spermatium indicate the belief that this struc- 
ture is the male apparatus, to be compared with a 
male conceptacle in Fucus (see p. 50). However, 
this function has not been demonstrated, and some 
regard them as spore-producing structures, in which 
case they are spoken of as pycnidia producing ^/"teleuTosporJ pro- 
pycnidios pores. If this is during basidia("promy- 
.,&, a sexual apparatus, j t "lia ") bearing basidio- 
'/I'-.-:" '/-' spores (sporidia ). 
would seem to be a ves- After TuLASNE . 
/rllfllwr^ tigial one. 
The other structure produced by the my- 
celium in the barberry leaf is the aecidium or 
diistercup. The aecidia usually appear in 
groups on the lower leaf surface, each opening 
upon the surface as a cup containing numer- 
ous simple sporophores bearing rows of spores, 
the aecidiospores (fig. 196). The scattered 
FIG. 195. Wheat rust: a 
spermogonium (producing aecidiospores that fall upon young wheat 
spermatia) arising from the plants germinate, the host is penetrated, and 
mycelium of the barberry leaf. mvcelium j 5 pro duced that begins to form 
After CHAMBERLAIN. 
uredospores. 
Polymorphism. In this life history the fungus passes through 
three distinct phases (the parasitic mycelium bearing uredospores and 
