DEPARTMENT OF AGRICULTURE


root. Locomotion of these animals with a double sheath around them
would be extremely difficult.
 Finally there are root-surface parasites with well developed loco-
 motive ability which nevertheless pass a sedentary existence on roots
 for extended periods. One group of these are ancestors of the kidney-
 shaped nematode previously mentioned. They are forms widely dis-
 tributed and because their long body is usually kept in the shape of a
 spiral they are called spiral nematodes (e.g. Helicotylenchus Steiner;
 Rotylenchus Filipjev). Their buccal stylet is quite long and strong and
 well fitted for inserting into plant tissue. Often the head and part of
 the anterior portion of the body are also inserted into the root (Fig.
 25). It is thought that this procedure is made easier by the retention of
 their bodies in a ventrally curved spiral of one to two turns. These
 spiral nematodes are still little known but are of wide distribution.
 Where numerous they may seriously interfere with plant growth. Helio-
 cotylenchus nannus Steiner is a small but very common species in the
 southeastern U.S.A., including Florida.
 Of similar behavior are the pin nematodes (genus Paratylenchus
 Micoletzky). The body of this genus, particularly that of the female,
 is venturally curved but to a lesser degree than in the spiral nematodes,
 possibly because they are much shorter. All members of this group are
 unusually small, and for this reason they frequently have been over-
 looked. It now appears that they are rather common, sometimes occur-
 ring in enormous numbers. The buccal stylet of the various species
 is always long, although the length differs considerably. This organ may
 be inserted into the plant tissue for a considerable portion of its length,
 a fact well shown in the folds of the esophageal canal when the stylet
 is retracted. The males in this group are all of a vestigial character,
 in some species very rare or even unknown, and their stylets are usually
 weak and degenerate (Fig. 26).

 MIGRATORY NEMATODES
 In contrast to the various types of fully or partially sedentary root-
parasitic forms, there exists a large group of migratory nematodes be-
longing to several different genera and families. These may be classed
into those forms that enter the tissues, move through the root and live
inside it, as well as others that puncture a root and feed on it from
the outside.
 The most important of the first mentioned group, i.e. those of endo-
parasitic habit, are those species belonging to Pratylenchus Filipjev and
related genera, or the so-called meadow nematodes. We know of at
least four different species of Pratylenchus from Florida alone. Meadow
nematodes are also widely distributed elsewhere. They attack the roots,
tubers, rhizomes, corms, or bulbs of various crops. Occasionally they
are also found in stems. A short, stout body and a strong buccal stylet