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cell-wall, and is sometimes simple, sometimes branched. At the place where 
the penetrating mycelium pierces a wall and enters a healthy wheat-cell 
there is developed, on the inside of the wheat-cell and surrounding and 
covering the penetrating mycelium, a callus-like structure (Fig. 17, e-g) 
which for brevity I shall term the “callus”. As the penetrating mycelium 
continues to grow, the ‘‘callus’’ grows pari passu. Where many penetrating 
mycelia develop near each other this “‘callus’’ may become very large 
Fic. 18.—H. No. 1: a, large ‘‘callus’’-formation, with many penetrating mycelia piercing the 
cell walls; 6, mycelium spreading over the wheat surface, and at many contact points producing 
appressoria and penetrating mycelia; c, penetrating mycelium of unusual form, and the ‘‘callus” 
rough. 
(Fig. 18, a) and complicated. The ‘‘callus’’ formation seems to be of the 
nature of a precipitation, probably resulting from toxic action, and a badly 
intoxicated cell can, in its protoplasmic disorganization, make numerous 
such deposits at points other than those of mycelial entrance. Thus in 
some instances the whole inner surface of a cell's walls may be thickly 
