Tech. C:2 



less obscured by debris, thus facilitating the examination for 

 nematodes in the Syracuse watch-glasses into which the nematode 

 suspensions have been drai«i off from the funnels. 



Small volumes of the water from the funnels should be withdrawn 

 periodically over a period of 12 to 2U hours, or longer if desired. 

 The water in the funnel should be maintained at a level submerging 

 the sample. 



Decanting and sieving is the method most used for samples ranging 

 up to a pint or, perhaps, a quart in size. The principle of decant- 

 ing involves washing the nematodes free from the soil particles by 

 roiling the sample in water, allowing the heavier soil particles to 

 settle momentarily, and then pouring off the supernatant liquid in 

 which the nematodes are suspended. 



Sieves operate in two ways in removing the various kinds and sizes 

 of nematodes from the nematode suspension which is poured through 

 them. If the diameter of a nematode is greater than that of the 

 opening of the sieve, the nematode is retained by the sieve. How- 

 ever, if the diameter of the nematode is less than that of the 

 sieve openings, the nematode will pass through, unless it is caught 

 by hanging across the wires of the sieve. This latter condition 

 exists with mfiny of the typically eel-shaped plant-parasitic nema- 

 todes which have body diameters less than the hi^mm. diameter open- 

 ings of the finest, or 325 mesh screen. The following table illus- 

 trates the relationship of the sieve mesh number to the sieve's 

 value in processing samples for nematodes: 



Mesh numbers: Effective for: Manner of operation: 



25 Retains debris and large Too large to pass 

 soil particles through sieve 



50-60 Retains cyst-forming Too large to pass 

 nematodes through sieve 



100 Retains eel-shaped 



nematodes of large size Most of the nema- 

 todes are caught 



200 Retains nematodes of only \-ihen they hang 

 most sizes except the across the wire mesh, 

 smallest forms with the exception 



of large nematodes 



270 Retains all nematode which may not pass 

 sizes; s'ilted water tlirough the 270 or 

 flows through readily. 325 sieve openings, 



325 Retains all nematode sizes; (as above) 

 sizes; silted water flows 

 flows through slowly. 



