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cell of a thread abutted against the wheat tissue (Fig. 17, g). So far as 
observed they differed from the usual mycelila cells only in shape. The 
appressoria are very numerous (Fig. 17, 6). They are usually produced 
only after the mycelium has grown to considerable length; not, as is the 
case with some fungi, immediately on emergence from the conidium. In 
See. 
Fic. 17: a, H. No. 1 on wheat, 24 hours after inoculation, showing mycelium arising from a conidium, 
an appressorium, and penetrating mycelium; 6, c, d, H. No. 14, showing appressoria, penetrating 
points, and ‘‘callus’’; e, f, g, h, H. No. 1: e, mycelium within cell, and with a penetrating mycelium 
reaching into an adjacent cell, a ‘‘callus’’ there resulting; f, mycelium ending squarely against a cell- 
surface, penetrating it and then being covered by ‘‘callus’’, and eventually penetrating this and 
the next cell-wall, the latter being thickened; g and h, similar to e. 
most cases the penetrating mycelium, viewed from above, appears as a 
minute bright point, or as if a minute hole had been pierced in the wheat 
cell-wall, much as is seen in the hyphopodia of Meliola (82) or on the 
appressoria of Gloeosporium (64) where penetration organs arise. Viewed 
laterally, the bright point of the appressorium is seen to mark the emer- 
gence of a haustorium-like strand which I shall continue to call the pene- 
trating mycelium. This structure is much thinner than the usual mycelium 
(see Fig. 18) and of different staining reactions. It penetrates the wheat 
