400 PHARMACEUTICAL BOTANY 
leaves some rust-red lines. The presence of the mycelium of 
the fungus in the intercellular spaces of the host does not kill the 
host directly or appear to stunt its growth, but the effect of 
_ the parasite on the host is seen when the grains mature. The 
grains are small and mushy, due to the fact that the nutrition 
of the host had been disturbed and the formation of starch in the 
grains inhibited. The mycelium is localized and gives rise 
underneath the epidermis to rounded egg-shaped spores attached | 
Fic. 297.—Spore forms of wheat rust, Puccinia graminis. A, Section through 
barberry leaf showing pycnia (spermagonia) on upper surface and zcia on lower; 
B, two urediniospores; C, germinating urediniospore; D, teliosorus showing several 
_ teliospores; E, single two-celled teliospore; F, germinating teliospore with four- 
celled basidium and two basidiospores; G, basidiospore growing on barberry leaf. 
(Harshberger, adapted from deBary.) 
to it by short pedicels. The spores are produced in such numbers 
that the space beneath is too’confined. As the long epidermal 
cells of grasses run longitudinally, the pressure of the spore 
masses from within causes the epidermis to crack and its edges 
become turned back. Through the resultant cleft the summer 
spores or uredospores (uriediniospores) are thrust out. These 
uredospores are orange-brown in color and covered with minute 
spines. ‘The mass of them has been called a uredinium. These 
spores are.detached from the pedicels and blown by the wind 
to healthy plants. After summer is over and dry weather 
