THE FUNGI 89 
that in order for the plant to complete its life-cycle, it 
was necessary that it should grow in turn upon both 
hosts. 
In the eastern United States there is another very 
conspicuous case of this hetercecism in the fungus caus- 
ing the enlargements 
on the twigs of the 
ted cedar known as 
*“cedar-apples”” (Fig. 
23, A). These mor- 
bid growths are due 
to the attacks of a 
fungus (Gymnospo- 
rangium) related to 
the wheat-rust, and 
in the spring the 
large orange-colored 
masses of spores are 
exceedingly conspic- 
uous, especially after 
a rain, when the 
gelatinous mass in 
which they are envel- 
oped swells up. The 
spores in these masses 
(B, C) give rise on 
germination to sec- 
ondary spores which 
germinate at once in 
case they fall upon 
Fic. 23 (Aicidiomycetes). — A, a branch 
of red cedar attacked by a parasitic 
fungus (Gymnosporangium), forming 
the excrescence known as a ‘‘cedar- 
apple’’; sp, masses of spores growing 
out from the surface of the cedar-ap- 
ple; B, two spores of Gymnosporan- 
gium, one of which is beginning to 
erminate ; p7, the young promycelium,; 
4 germinating spore which has given 
tise to a promycelium from each cell; 
the secondary spores, x, produced upon 
the promycelium do not germinate upon 
the cedar, but produce upon the haw- 
thorn the so-called ‘‘ zcidia,”’ or clus- 
ter-cups; D, a leaf of cockspur thorn, 
with two groups of cluster-cups, ae; 
E, section through an ecidium of 
another rust (Uromyces caladii). 
the young leaves of the wild crab-apple or hawthorn, 
but will not grow upon the cedar. 
The fuhgus pro- 
