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CHAPTER XI. 
INFECTION OF THE HOST-PLANTS BY THE USTILAGINE&. 
THE manner in which the Ustilagineze gain admission into 
their respective host-plants has been studied very carefully 
by many botanists, but is not yet fully understood. With 
those species which affect the flowering parts of annual 
graminaceous plants, such as 77/etia tviticd and U. segetum 
on wheat, it is noteworthy that not only are all the blossoms 
or fruits upon an ear affected, but also all the ears which 
arise from one plant. It is very exceptional ever to find one 
sound ear upon a plant of which the others are diseased ; in 
like manner, it is very unusual to find a sound kernel upon 
an ear in which the other kernels are affected. Coupled with 
the fact that in diseased plants the mycelium of the fungus 
can be found in all parts of the axis, it is obvious that the 
parasite gained admission into the plant at an early stage 
of its growth. Kiihn * specially investigated this point with 
T. tritic¢, and found, in very young wheat seedlings, that the 
mycelium was present in them. Hoffmannt came to the 
conclusion that the spores entered between the split in the 
young sheath and the rootlet. He also figures the spores 
. forming a mycelium which enters the stomata of the young 
* Kiihn, oc. cit., pp. 48, 49. 
t Hoffman, ‘ Flugbrand,” pp. 202-206, t. xiv. figs. 14-18. 
