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 stiilpen, wie in eine Scheide von bald 

 grosserer 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 



FIG. 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 



