June 15, 1914 
Citrus-Root Nematode 
219 
of plants from Florida and also a variety of plants collected in the vicin¬ 
ity of Citrus groves in California by Drs. T. J. Briggs and H. T. Shantz, 
of the Bureau of Plant Industry, both of whom have taken an active 
and exceedingly helpful interest in the nature of the Tylenchulus disease, 
on account of its possible bearing on malnutrition of Citrus trees, a sub¬ 
ject to which they are giving special attention. Hundreds of samples 
of roots of a great variety of plants other than Citrus, collected from 
various parts of the world, have been examined by the writer without 
disclosing any specimens of 
Tylenchulus. 
We may take it as fairly well 
established that Tylenchulus 
semipenetrans is a parasite 
peculiar to Citrus roots, occur¬ 
ring in all parts of the world 
where Citrus trees have long 
been grown. 
In searching for Tylenchulus 
semipenetrans care must be 
taken not to confuse it with 
other species of nematodes. 
Fortunately its characters are so 
very well marked that there is 
very little difficulty in establish¬ 
ing its identity if adult females 
can be found (see fig. 1). On 
the other hand, unfortunately, 
its larval forms closely resem¬ 
ble those of certain other spe¬ 
cies of nematodes—so closely, 
indeed, that they can not be 
identified with certainty, except with the aid of an oil-immersion lens 
skillfully used by a person conversant with the characteristics of the 
various genera and species of nematodes. Much the same may be said 
of the males, as these also are rather exceptionally hard to identify with 
certainty. The fitness of these remarks will appear when it is stated 
that already the writer's examinations, directed primarily at Tylenchulus 
semipenetrans , have revealed the presence about the roots of Citrus trees 
in various parts of the world of toward 100 different species of nematodes, 
many of which are spear-bearing and have larval forms which might 
easily be confused with those of Tylenchulus by one unskilled in the 
art of identifying nematodes species. 
Whenever larval nematodes from near roots of Citrus are being exam¬ 
ined with the object of ascertaining whether or not they belong to the 
species Tylenchulus semipenetrans , the observer should keep in mind that 
Fig. 3. —Citrus root attacked by the parasitic nematode 
Tylenchulus semipenetrans , magnified 5 diameters. The 
parasites are shown at a. They are shown black, but 
in reality are yellowish or brownish. Compare with 
figure 2, and note that owing to the presence of the 
parasite the feeding roots may become somewhat 
enlarged and irregular and that the outside portion of 
the root is somewhat separated from the axial portion, 
as shown at b. When the roots are agitated in water, 
the outside portion sometimes becomes loosened in seg¬ 
ments which will slide on the axial portion b , some¬ 
what as beads slide on a string. 
