FUSARIUM 



491 



being prevented from ascending the stem, owing to the 

 vessels being filled with mycelium. The root is the part 

 first attacked, the fungus entering through the root-hairs 

 and eventually forming a dense mass of mycelium in the 

 vascular portion of the root and stem for some distance 

 above the collar. If at this stage the stem is split open just 

 above the collar, the vascular bundles are seen to be brown 

 in colour, due to the presence of a brown substance in the 



FlG. 148. Fusarium lycopersici. i, Diplocladium 

 stage ; 2, Fusarium stage ; 3, resting spores. All 

 highly mag. 



vessels, caused by the mycelium. Shortly after the plant 

 has drooped, the portion of stem just above ground becomes 

 more or less covered with a delicate, white film of hyphae. 

 This is the first conidial condition of the fungus, known as 

 the Diplodadium stage. This is followed by a second or 

 Fusarium stage, which originates from the same mycelium 

 that produced the first stage. Numerous strands of mycelium 

 spread from the roots into the soil, and there form resting- 

 spores which remain in a passive condition in the soil until 



