Tech. A: 6 



nematodes from the saimile occurs when the nematodes, moving 

 about in the water-soaked sample, eventually reach and pass 

 through the porous boundry which, however, holds back the soil 

 or plant particles. The nematode r; sink to the sides of the 

 funnel, and gradually move or drift to the apex of the funnel 

 and accumulate in the funnel stem and rubber tubing just above 

 the clamp. Releasing the clamp at intervals over a period of 

 hours or days permits collection of the nematodes, concentrated 

 in a relatively small voli:mie of water and reasonably free from 

 soil and plant debris. 



There are many variations in actual practice, all utilizing the 

 principle of the Baermann funnel; there are more variations than 

 it is possible to describe here. However, a few generalizations 

 are offered which will be helpful in \inder standing the signifi- 

 cance of the results obtained and in devising improvements. 



Most of the nematodes which come through the porous barrier do 

 so only because of their own activities. Nematodes which are 

 nonaally not very active or which are sluggish because of 

 insufficient oxygen, starvation, excessive bacterial contamina- 

 tion, or too cold a teraperatui^e are not likely to be recovered 

 in high percentages. Random movement is probably the rule rather 

 tha.'i tropistic movement, so the larger the surface area to vol- 

 ume ratio of the s;imple, the greater the chances of recovery of 

 nematodes. The shorter the distance from the sample to the 

 claraped-end of the furmel and the steeper the walls of the fun- 

 nel, the higher the collection rate. It is, of course, obvious 

 that the sample itself should be crumbled or cut into small frag- 

 ments to facilitate fr-eeing the nematodes. 



In practice, funnels of about five to six inches in diameter are 

 satisfactory for small samples or for residues from the sieves 

 placed in the funnel for further cleaning. Funnels of about 

 eight inches in diameter are good for moderate sized soil or 

 plant samples which are placed directly in the funnel without 

 previous sieving. Verylarge funnels made of sheet metal can be 

 used to recover nematodes from large samples put to soak in the 

 funnel. Funnels may be of glass, metal, or plastics. 



The steeper the angle of the conical section, the larger the 

 bore of the stem, and the shorter the stem, the better; both as 

 an aid to recovery of more nematodes and for ease of cleaning 

 after each use. Guard against using funnels designed for filter- 

 ing purposes which have a constriction in the bore of the stem 

 at the point of its union with the conical part of the funnel. 

 Cut the stem short, leaving support for attaching the tubing. 

 Spring-action hose clamps are preferable to the screw-type, in 

 order to have adequate control over the small amoimts of liquid 

 to be draim from the funnel. 



Supports for the soil or plant samples, Xirhen placed in the funnel, 



