CHAPTER Iii. 
FUSARIUM UDUM N. SP., THE CAUSE OF PIGEON-PEA WILT. 
The repeated examination of the roots of wilted pigeon-pea 
plants in all stages of the disease, carried on during the course of 
the investigations described above, left practically no doubt that 
the disease was a typical Fusarium wilt. Attempts to prove its 
connection with Fusarium stages of the two Hypocreaceous fungi 
found on the bark, the Nectria found at Dehra Dun and Neocos- 
mospora vasinfecta, having failed, it remained to look elsewhere. 
The number of soil organisms that may be obtained from dead 
vegetable matter in the soil (such as the surface of the roots of a 
dead or dying plant) is greater than would be anticipated by any 
one not accustomed to the specific examination of soils for fungi. 
In any locality several are sure to be so common as to be found on 
almost any root examined, and amongst these are Fusaria probably 
belonging to several different species. It appeared an endless mat- 
ter to hunt through these for possible parasites. If, however, the 
superficial forms could be excluded or destroyed, it seemed likely 
that the true cause could be induced to give a comparatively 
pure surface growth by appropriate treatment. The following 
procedure was, therefore, adopted to isolate any truly internal 
organisms that might occur in diseased roots. 
A short length of tap root from a just wilted seedling was cut 
off with a flamed scissors and the presence of the internal mycelium 
determined by sectioning the end of one or other of the rejected 
pieces. The root was washed thoroughly, first in tap water and 
then in several changes of distilled water, being well rubbed between 
the fingers to remove irregularities where particles of soil might 
lodge. It was then seized in sterile forceps, dipped in absolute 
alcohol for about 5 seconds, the alcohol flamed off and the root 
