350 PRINCIPLES OF SOIL MICROBIOLOGY 



Rhabdolaimus, found in moist soil. 



Cephalobus, commonly found in the soil, can be grown on decomposing or- 

 ganic matter. 



Teratocephalous, omnivagous, found in moist soil. 



Bastiana, largely soil forms. 



Tripyla, found in soils rich in undecomposed organic matter, not very 

 abundant. 



Alaimus, well distributed in the soil, especially in moist and forest soils. 



Prismatolaimus, represented in the soil by some species. 



Monohystera, omnivagous, found in moist soils, some feed on diatoms. 



Trilobus, seldom found in moist soils, feeds on diatoms and rotatorians. 



Various Mermithidae are also found in the soil. 



A number of other genera, like Bunonema, Tylopharynx, Archionchus, Euty- 

 lenchus, etc., are found in the soil less abundantly. 



What is known of the nutrition of free-living soil nematodes has 

 been reviewed in detail by Menzel. 22 He found that Mononchus papil- 

 latus, when brought together with Tylenchus sp., Plectus auriculatus, 

 Tripyla media and Anguillula aceti, killed these forms either by swal- 

 lowing them completely or by sucking out their contents. Steiner and 

 Heinley grew the Mononchus papillatus in water containing some soil 

 and placed in concave slides. It is important to use a small amount 

 of soil free from excess of organic matter so as to prevent the rapid 

 development of bacteria. The medium should be frequently renewed. 

 Heterodera, Rhabditis and Anguillula were used for food. As many as 

 83 Heterodera radicicola were killed in one day by one Mononch; during 

 a life time of about 12 weeks, one animal killed 1332 nematodes. It is 

 possible that this number may be much larger under natural condi- 

 tions (No. 151, PI. XVIII). 



Steiner and Heinley, therefore, brought further weight to the sug- 

 gestion of Cobb that the predatory Mononchs could be used to control 

 the plant parasitic forms, when the latter are still free in the soil. How- 

 ever, we must keep in mind that the mere introduction of an organism 

 into the soil is not sufficient to insure its development; the soil should 

 be treated in such a manner as to favor the development of the bene- 

 ficial organism and discourage the development of the injurious forms. 23 



The role of nematodes in the soil may, therefore, consist of the fol- 

 lowing processes: 



1. Consuming and destroying cultivated plants, often causing considerable 

 damage. 



22 Menzel, R. Uber die Nahrung der freilebenden Nematoden und die Art 

 ihrer Aufnahme. Ein Beitrag zur Kenntnis der Erniihrung der Wurmer. Ver- 

 handl. Naturf. Gesell. Basel., 36: 153-188. 1920. 



"Baunacke, 1922 (p. 344). 



