2 l8 
Journal of Agricultural Research 
Vol. II, No. 3 
Since that time the writer has given some attention to the anatomy, 
life history, and distribution of this species, and in cooperation with the 
Office of Foreign Seed and Plant Introduction, Bureau of Plant Industry, 
and its correspondents abroad, notably the American consuls stationed 
in Citrus-growing regions, has shown that it is probably world-wide in 
its distribution. Sam¬ 
ples of the feeding roots 
of Citrus trees, such as 
Tylenchulus infests (figs. 
2, 3), were sent to these 
various foreign corre¬ 
spondents, with the re¬ 
quest that they forward 
to Washington from their 
localities similar roots 
taken from trees that 
appeared to be suffer¬ 
ing from malnutrition— 
trees that were off color. These roots on being received at the Depart¬ 
ment were examined, with the result that this Citrus parasite was 
found to infest Citrus roots at Valencia, Spain, and at Malta. Pre¬ 
viously, the nematode had been found in small numbers in one 
locality in Florida. Through the courtesy of Mr. Charles O. Chambers, 
of Gosford, New South Wales, Aus¬ 
tralia, roots of Citrus were obtained 
from his locality. These proved 
also to be Tylenchulus-infested. 
Similarly, roots of Citrus sent from 
Haifa, Palestine, through the cour¬ 
tesy of Mr. Aaron Aaronsohn, were 
found infested. Particular men¬ 
tion should be made of the numer¬ 
ous specimens of roots of Citrus 
and soil received from Mr. R. S. 
Vaile, Horticultural Commissioner 
for Ventura County, Cal., as well 
as from Messrs. J. W. McTane and 
R. L. Piemeisel, of the Bureau of 
Plant Industry. The evidence 
sho;ws this parasite to occur in 
widely separated parts of the world, and it probably occurs in every 
region where Citrus trees have been successfully grown for any consid¬ 
erable length of time. 
It appears also that Tylenchulus semdpenetrans is peculiar to the feed¬ 
ing roots of Citrus trees. • It has never been found attacking any other 
species of roots, although careful search has been made for it on a variety 
Fig. 2. —Healthy Citrus root magnified 5 diame¬ 
ters. Note the size and form of the healthy root 
endings. Compare with figure 3. 
Fig. 1 . —Tylenchulus semi penetrans: Mature and half-grown females, 
with their head ends permanently embedded in the feeding root 
of a citrus tree. This is a plant parasite similar in many ways 
to the notorious gallwonn Heterodera radidcola. a, Tail end; 6, 
vulva; c, excretory pore; d t e, egg in uterus. 
