222 
Journal of Agricultural Research 
Vol. II, No. 3 
ingly thrown out a new shoot farther back, as often happens in such 
cases, the new generation of young females 
make their way to this new shoot. This 
supposition accords with what is known about 
the growth of roots in general when injured 
by disease-producing organisms and is in 
harmony with the weak muscular powers of 
the Tylenchulus. 
Although the movements of Tylenchulus 
semipenetrans are so feeble as to make it 
seem quite unlikely that it travels any great 
distance by the aid of its own muscular 
powers, its small size is in favor of its trans¬ 
portation from place to place in the soil by a 
great variety of agencies, such as soil water, 
subterranean insects, worms, and burrowing 
animals. In this way it may be carried to 
considerable depths in the soil and doubtless 
will be found attacking Citrus roots, however 
deep the latter penetrate. When cultural 
operations bring Tylenchulus semipenetrans to 
the surface and these cultural operations are 
followed by irrigation, the eggs and free-living 
young stages may be carried from tree to tree 
in the same grove by the irrigation water, or 
from orchard to orchard, or even occasionally 
from district to district; in fact, wherever 
Citrus fruits are grown under irrigation, the 
irrigation water is undoubtedly one of the 
principal agents in distributing the pest after 
it has once become established through the 
planting out of infested nursery stock. 
Tylenchulus semipenetrans is comparatively 
sensitive to temperatures much above those 
of ordinary soil. When eggs, larvae, or adults 
are placed in water above ioo° F., they are 
quickly affected, and at 130° F. are killed. 
Immersion in water at 140° F. causes almost 
instant death to all forms of the organism. 
This fact was demonstrated and utilized in 
studies of the life history. 
To follow the development of the eggs and larvae, they were placed in 
capsules constructed in accordance with the explanation accompanying 
X400 
Fig. 6 .—Tylenchulus semipenetrans: 
Larva, soon after hatching from 
the egg. Note the absence of the 
anus, a , I4p region; b , spear; 
c, 3-bulbed base of spear; d, lumen 
of the oesophagus; e, median oe¬ 
sophageal bulb;/, nerve ring; g, 
posterior oesophageal bulb; h t be¬ 
ginning of the intestine; /, large 
intestinal granule; k, small intes¬ 
tinal granule; n, excretory pore; 
i, terminus. 
