PLANT NEMATODES THE GROWER SHOULD KNOW 33

 closely related and difficult to differentiate. The adult female has a
 swollen, spherical, lemon- or pear-shaped body, unlike most other nema-
 todes, while the male retains a threadlike body shape.
 But this group is not the only one in which sedentary life has
 resulted in transformation of the female by globular inflation. The same
 phenomenon is seen in other genera of quite different origin and rela-
 tionship; an outstanding example is Nacobbus, a form only recently
 described by Thorne and Allen from California. Here the female has a
 protruding vulva of such length that it resembles a tail; this enables it
 to deposit the eggs outside the root since the protruding tail-like vulva
 appears always so located as to reach the root surface.
 The citrus nematode (Tylenchulus semipenetrans Cobb) is still an-
other example of a swollen, sedentary type of root parasite. It belongs
to still a different taxonomic group from the two already mentioned. In
this instance the roots are attacked from the surface and only the elon-
gated anterior portion of the body penetrates the root tissue, while the
posterior part swells, as shown in Fig. 20. Here again, however, the
male is of very different shape and appears not to feed at all. In fact
it hardly increases in size while developing from the larval to the adult
stage.
 There is still a fourth type of swollen sedentary root parasitic nema-
tode, the kidney-shaped nematode (Rotylenchulus reniformis Linford).
The parasitic female is attached to the root surface but its body is sur-
rounded by a spherical structure which it forms for itself by secreting
a glabrous substance which also surrounds the eggs and cements together
adjacent soil particles. We located this interesting species recently from
Florida on roots of tomato and coffee weed (Cassia tora L.) sent to us
from Quincy. As in the citrus nematode, the anterior portion of the
body of the female is elongated and is inserted into the root while the
reniform, main part protrudes from the surface. The male in this case
also remains small and its body is not swollen. Because of its bubble-
shaped glabrous enclosures covered with soil particles, Rotylenchulus is
very difficult to see and may easily be overlooked or mistaken for globu-
lar soil agglutinations adhering to the root (Fig. 21).
 It is obvious that all these sedentary nematodes with inflated and
obese bodies that become fixed in or on a root lose their motility and
are unable to change their position and migrate. If roots containing such
stationary parasites are uprooted and destroyed before the parasites are
fully grown or before they have produced eggs, the source of infection
is removed. Control of certain of these nematodes by a trap- or catch-
crop is based on these considerations. Since only the preparasitic, larval
stage of these sedentary forms is able to migrate, the spread of these
various types by their own means is very restricted. Thus long distance
travel is entirely one of transportation by such carriers as wind, water,
and particularly man, who spreads them with plant material of all kinds
and with soil.