Nematode Diseases of Plants. 
BY PROF. EARNEST A. BESSEY. 
Mr. President, Ladies and Gentlemen: 
I wish to speak to you today about 
nematodes. In the first place, it may be 
well to attempt to explain to you just what 
a nematode is, although most of you are 
familiar enough with the work of one of 
them, the root-knot. Nematodes or ell- 
worms as they are sometimes called, are 
low animals, slender and worm-like, at 
least when young. Like the true worms 
they have no legs nor wings at any stage 
of their development. They differ from 
the latter in not being segmented and in 
having no jaws. They consist essential¬ 
ly of a tube-like skin lined with muscles; 
inside this is another tube, the alimentary 
canal, with various modifications along its 
course to act as gizzard, stomach, etc. 
Add a very simple nervous system and 
you have nearly all the essential features 
of a nematode. They should never be 
confused with the segmented earth-worms 
nor with the larvae of various insects, 
also, but erroneously, called worms. 
Many species of nematodes are par¬ 
asitic in animals, as, for example, the 
roundworm of the horse, the hookworm 
and trichina of man; many others live 
in various locations, both in the earth 
or in fresh or salt water, on decaying or¬ 
ganic matter, a wellknown example being 
the harmless vinegar-eel; while still 
others attack living plants. The latter are 
entirely harmless to animal life, so that 
we need not fear their presence on that 
score. They are bad enough as it is,* how¬ 
ever. 
With the exception of some that are 
parasitic in higher animals, nematodes 
are mostly minute. Those that attack 
plants are rarely over one-eighth of an 
inch in length, while some are many times 
smaller. Were it not for their great num¬ 
bers they would scarcely require serious 
attention. 
The principal disease of plants due to 
nematodes, at least in this country, is root- 
knot, in which the nematodes live within 
the root, causing it to enlarge, forming 
the characteristic knots. In addition to 
this di'sease, other species of nematodes 
cause abortion of the flowers of grasses, 
distortion of leaves and flowers through 
their presence within the stem, stunting 
and malformation of plants through 
nematodes living within the stem, killing- 
out of spots in leaves through nematodes 
in the tissues at these points, and injured 
canker-like spots on the roots. The lat¬ 
ter are caused by nematodes attacking the 
roots from the outside without entering- 
them. 
The life history of the root-knot nema¬ 
tode is in short as follows: The eggs, 
which are about 1-300 inch long, hatch 
into little larvea about i-ioo inch long, 
and about 1-2000 inch thick. These pos¬ 
sess at the anterior end, a stout spear. 
Crawling around in the soil they finally 
find roots, perhaps not for weeks after 
