78 BUREAU OF PLANT QUARANTINE [July-Sept. 
Another indication of eelworm attack is a corkscrew twisting of the leaves, or 
the leaves may become sickle-shaped. In some of the narrow-leaved varieties 
in which spikkels are not prominent there is often a peculiar spearhead broadening 
near the tips of the leaves. 
The presence of numerous, regular swellings in the surface of the leaf often 
without a conspicuously lighter green color, or sometimes a few but abrupt swell- 
ings of light green color, is more likely to be an indication of hot-water treatment 
than of the presence of eelworms. 
Microscopic diagnosis in field. — When leaves having spikkels and other mal- 
formations apparently indicating the presence of eelworms are found, the next 
step is to determine whether or not eelworms (bulb nematodes) are actually 
present. This necessitates a microscopic examination of the suspected tissue. 
The technic is rather simple but must be performed carefully and with close 
observation to avoid missing the nematodes. The procedure is based on the 
fact that fluid is the eelworms' medium of travel, and consists in tearing up 
suspected eelworm-infested tissue in a very small amount of water. No elaborate 
equipment is necessary, although a field binocular of about 15 diameters mag- 
nification is desirable for examining small spikkels, as such spikkels may contain 
only one or two nemas, and when in such small numbers they are hard to pick out 
with a hand lens. The binocular has a greater field of vision than an ordinary 
compound microscope and has advantages over a hand lens in that it permits 
continued observation of the culture even while both hands are being used for 
dissecting the suspected tissue; thus any nemas that appear in the water may be 
seen before they have a chance to swim out of sight or reenter the tissues. In 
the case of large spikkels and the yellow streaks referred to above, there are 
usually so many nemas present that not all of them can hide during the short 
period required for laying down the dissecting needles and focusing a hand lens. 
In fact, with the latter class of material, one can sometimes see the nemas by 
simply focusing the hand lens on the leaf as it is broken lengthwise along the 
yellow streak. 
A small section containing the spikkel or other suspected area is cut from the 
leaf with a sharp knife and placed in a watch glass. Flat surfaces such as slides 
are not satisfactory for making dissections of leaf tissue although they are excel- 
lent for use during dormant bulb inspection. With dissecting needles ready 
(old-fashioned darning needles do very well) a few drops of water are placed on 
the section of suspected tissue, just enough water to cover the material but not 
enough to have any. part of it completely out of focus. The section of leaf tissue 
is then torn apart, preferably first dow T n through the middle of the spikkel with the 
dissecting needles. If a binocular is being used the watching for nemas and the 
shredding of tissue goes on simultaneously, but if one is using a hand lens it is 
desirable to shred a few fibres and then closely examine the material, and keep 
alternating the shredding and examining until the nemas are discovered. If one 
shreds up too much tissue before examining the culture with the lens, there is 
likelihood of the nemas hiding among or reentering the tissues. 
If no nemas are found in the first section taken from the suspected leaf, another 
section is taken just below and torn apart more carefully. If the spikkels or other 
malformations referred to above have been correctly identified in the field, it is 
almost certain that nematodes will be found if the material is properly examined. 
A good, clear light is essential but there is such a thing as too much reflection; also 
too much magnification. In clear water a full-grown nema is quite visible to the 
naked eye, and in proper light a magnification of 10 diameters is sufficient to 
allow accurate identification by the typical shape. 
If the material being examined is characterized by any rotting tissue or includes 
particles of soil or debris outside the plant, the nemas found may be saprophytic 
or free-living forms. The bulb nematode may usually be distinguished from 
other species by its eellike shape and manner of movement. It is more slender 
than saprophytic nemas and less active. Other characteristics are shown on the 
plate at the conclusion of this circular. That plate will also aid in distinguishing 
Tylenchus dipsaci from the other parasitic species Aphelenchoides subtenuis and 
A. parietinus. So far as possible it is desirable that diagnosis should be con- 
firmed by specialists as to at least one specimen from each grower's premises, 
although experienced field inspectors become so familiar with the characteristics 
of bulb nematodes that their diagnosis by the methods indicated is usually con- 
firmed by specialists. 
The nematodes are likely to leave the spikkel very soon after the leaves are cut 
and are almost sure to be absent from the spikkel itself if several hours have 
elapsed. In this case the tissue below the spikkel is examined instead of the 
