Nematode Root Parasite — LINFORD, et al. 
115 
pounds. Survival in subsoil or in non-fumigated 
spaces between beds, or both, is the probable 
explanation. Similar reinfestation occurs with 
other nematodes. 
PARASITIC HABIT 
Paratylenchus minutus is chiefly ectoparasitic 
in the young mature zone of roots. This has 
been determined by microscopic examination of 
the undisturbed association of living nematodes 
with roots, utilizing methods described in detail 
elsewhere (Linford, 1942&). Briefly, roots are 
grown in infested soil or other fine granular 
media against a thin coverslip and are then 
examined under the compound microscope with 
incident light. A 40X water-immersion objec- 
tive lens permits useful magnifications up to 
600 diameters. This method of study has defined 
the general patterns of the feeding process and 
of host response. Microscopic examination of 
stained and cleared roots has yielded informa- 
tion on occurrence within roots. 
Paratylenchs are attracted to the piliferous 
zone where, typically, the larvae and females 
remain on the surface to feed by inserting the 
stylet tip into epidermal cells or root hairs 
(Fig. 3). Males often are observed among 
them but are unable to feed. The process of 
puncturing a cell wall has not been observed; 
but it probably is accomplished rapidly, in con- 
trast with the somewhat prolonged effort re- 
quired by larvae of Heterodera marioni (see 
Linford, 1942^: 582), because few tentative 
thrusts of the paratylench stylet have been seen. 
The majority of nematodes found with the 
stylet tip inserted into a cell have been in proc- 
ess of feeding as shown by rhythmic pulsation 
of the median esophageal bulb, with its valve 
opening and closing rapidly. 
Periods of sucking alternate with and are pre- 
ceded by periods of rest during which the me- 
dian bulb is inactive or only twitches occa- 
sionally. Such periods may vary from a few 
Fig. 3. Two Paratylenchus minutus feeding on root hairs of cowpea growing against the coverslip in an 
observation chamber. Both nematodes have their stylet tips inserted into living root hairs. X 1,500. 
