88 FUNGOID DISEASES 



VIII. Dry Rot {F2isariuni solani). Fitngi 

 Imperfecti ; Order : Moniliales. 



Some ten to fifteen species of Fttsariuni are 

 capable of causing rot of potato tubers, some 

 causing wet, others dry rot. The name Fusarium 

 solani has probably been applied rather indis- 

 criminately to all of these. Though the fungus is 

 widespread, the damage caused is small compared 

 to that caused by some of the other fungi. 



Symptoms. — Shrivelling up of the contents of the 

 potato, causing cavities on the surface, in which a 

 whitish grey felted mass of mycelium may be seen. 



Cause. — The mycelium noted above is that of 

 F^csarhcm solani, which grows in and betw^een the 

 cells, destroying the cell tissue but leaving the starch 

 grains unattacked, though some of them may, at 

 the later stages, have the mycelium penetrating 

 them. Entrance to the potato usually takes place 

 through some wound, but Wehmer has shown that 

 the hyphae are also capable of entering potatoes 

 which are perfectly intact. 



The hyphse are long and fine with cross walls. 

 The spores are very characteristic ; being long, 

 slender, pointed, cresent shaped, and multicellular. 



Note. — Phellomyces sclerotiophorus also causes a dry rot. 

 Here again the starch grains are very little changed. 



Pi'evention. — Unfortunately the fungus is so 

 widespread that little can be done. The "pies" 

 may be opened and the diseased tubers picked out. 



