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CHAPTER XI. 



INFECTION OF THE HOST-PLANTS BY THE USTILAGINE.F;. 



The manner in which the Ustilagineae 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 Tilletia tritici and U. segettun 

 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. Klihn * specially investigated this point with 

 T. tritici, and found, in very young wheat seedlings, that the 

 mycelium was present in them. Hoffmann t 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, loc. tit., pp. 48, 49. 



t Hoffman, " Flugbrand," pp. 202-206, t. xiv. figs. 14 18. 



