228 
Journal of Agricultural Research 
Vol. II, No. 3 
these latter in swallowing organisms of relatively large size. It is a 
natural supposition that the minute teeth in the pharynx of the Mon- 
onchus serve a similar purpose. These minute teeth do not occur in 
the Mononchus here mentioned as feeding on Tylenchulus. 
The writer has in his possession a specimen of Mononchus caught in 
the act of swallowing another nematode. The Mononchus holds its prey 
in the grip of its “jaws” and partially swallowed. The phenomenon 
reminds one of the not infrequent discovery of serpents with half- 
swallowed birds in their maws. The writer has also observed aquatic 
species of Mononchus whose intestines contained only the remains of 
rotifers, indicating that the species of Mononchus do not feed exclusively 
upon other nematodes. 
These definite observations on the Mononchus lend new interest to the 
study of this genus, which is estimated to contain a very considerable 
number of species, probably a hundred or more when all shall have been 
enumerated. Upward of 20 species are known to the writer. The 
examination of almost any good collection of soil-inhabiting or fresh¬ 
water nematodes is pretty sure at the present date to reveal one or more 
hitherto unknown species of Mononchus. Both on the ground of the 
number of species of Mononchus and the number of their individuals the 
matter is one well worthy of further observation. 
There are other nematode genera that on structural grounds may now 
be suspected to be vermivorous, or at any rate carnivorous. 
CONCLUSIONS 
There can be no doubt that Tylenchulus semipenetrans is an injurious 
parasite. There is conclusive evidence that it kills the feeding roots of 
Citrus trees. The roots die either as a direct result of the attack of this 
parasite or of the attack of other organisms following in its wake; in 
other words, the nematode is a primary cause of the death of the feeding 
roots. Many cases have come under observation in which it was apparent 
that, had it not been for the nematode, the roots would have remained in 
a healthy condition. The evidence along these lines is of the same char¬ 
acter as that which is relied on in demonstrating injuries due to insects 
and other macroscopic parasites. 
The extent of the damage which may be properly charged up against 
this parasite is a different matter, and it will be necessary to collect 
evidence along this line for several years before a final statement can be 
made. Up to the present the data obtained indicate unquestionably that 
the investigations should be continued. 
The writer's long experience with numerous fungous diseases of the 
Citrus family has led him to conclude that, though a few of these diseases 
are very harmful, most of them are of minor importance. There are many 
fungous diseases of the bark, foliage, and fruit of Citrus trees of such a 
character that they are easily controlled. In many cases all that is 
