166 Eelworms [CH. XIII 
regarded as living saprophytically on decaying matter, 
but it is possible that they hasten the destruction of 
the plant. Parasites may readily be distinguished 
from free-living forms, by the possession of a retractile 
spine-like process at the head end which is used for 
penetrating plants (see Fig. 51(C). 
The parasitic forms are comparatively much thinner. 
They are very sluggish in their movements as compared 
with most free-living forms. Many of the latter have 
long tails which help them to move quickly. 
Tulip-rooted Oats. 
Tulip root in oats is due to two causes, one of 
which, frit fly, has already been studied. The other 
cause is due to an eelworm known as T'ylenchus dipsaci 
(formerly devastatrix). Sometimes both are found in 
the same plant. The two diseases are very similar in 
appearance (cf. Figs. 38 and 52). On examining diseased 
plants containing frit fly we usually find (not in the 
earliest stage) in addition to the frit fly a number of 
free-living eelworms. If the tulip root is due to 
Tylenchus we shall find a considerable number of 
Tylenchus together with a number of free-living forms. 
We are now in a position to distinguish T'ylenchus from 
the free-living forms (see Fig. 51). In looking for 
eelworms we simply tease a small portion of the stem 
in water on a slide and examine it under the microscope. 
A Tylenchus very similar to J. dipsaci in appear- 
ance is one of the causes of “clover sickness” and 
is held by many authorities to be the same as that 
which attacks oats: nevertheless healthy crops of oats 
have been grown after clover attacked by the eelworm 
Tylenchus sp. 
