135 
dass der Faden, sobald seine Spitze in das Innere der Zelle tritt, nicht 
frei in dieses hineinwachst, sondern von den inneren Schichten der Zell- 
wand, welche sich gleichsam aus sttilpen, wie in eine Scheide von bald 
grésserer bald geringerer, oft sehr betrachtlicher Starke eingeschlossen 
wird und in dieser bis zur nachsten Zellwand weiter wachst.’’ Brefeld 
describes very similar conditions, including much thickening which is 
of yellow color, but instead of interpreting it as an enclosing sheath he 
regards it as wholly due to thickening of the walls of the mycelium itself. 
He moreover states that this phenomenon is indicative of conditions 
in the host, as too great age, that are unsuitable to infection, and that it 
is not in evidence when the host is in fully susceptible condition. Which- 
ever may be the true interpretation in the case of cereal smuts, I am 
convinced that in case of Helminthosporium the ‘‘callus”’ is produced _by 
Fic. 23.—Infection by H. No. 1, 24 hours after inoculation, showing 
thickening of the wheat cell-walls by deposition on their inner surfaces. 
(Text citation at top of p. 131.) 
the wheat-cell, and is not part of the mycelium. Ravn (91), describing 
the reactions to the intercellular mycelium of Helminthosporium in cereals, 
states that a thickening appears upon the cell-wall of the host, resembling 
a drop segregated from the cell, and that several such thickenings may be 
seen upon one cell, sometimes filling the intercellular spaces completely. 
They seem to differ from those that I describe (Fig. 17), however, in posi- 
tion, since they are without, not within, the cell, and in composition, as 
those noted by Ravn take aniline stains readily. 
Ravn (91, fig. 23) describes an appressorium very much like that 
which I find and states that the mycelium from it enters the epidermal cell, 
where it so increases that it may fill the cell; then makes its way to the 
intercellular spaces and grows there exclusively, never again entering 
any of the cells even by means of haustoria. It therefore appears from 
his statements and figures that the Helminthosporiums with which he 
