348 PRINCIPLES OF SOIL MICROBIOLOGY 



2. Some feed on the tissues and fluids of healthy or injured plants, thus be- 

 coming injurious to higher plants; these include Tylenchus, Helerodera, Aphe- 

 Icnchus (Nos. 148-149, PI. XVIII), some of which are truly parasitic and others 

 are semi-parasitic (like Hoplolaimus) or facultative parasitic. 



3. Some are parasitic on animals, especially invertebrate soil forms. 



4. Some feed both on plants and animals, like Dorylaimus. 



5. Some are carnivorous and predatory, feeding on other nematodes, like 

 Ironus, Tripyla, and especially the numerous species of Mononchus. Mononchus 

 papillalus, for example, can feed readily upon Heterodera radicicola 10 (Nos. 150- 

 151, PI. XVIII). 



The maximum number of nematodes was found 13 in Tyrol soils in 

 August, reaching 320 per 10 cc. of soil; the number then dropped 

 rapidly and reached the lowest point in November, with 23 animals 

 per 10 cc. It remained at a low level during the winter months and 

 began to increase again in February. On the average, 120 nematodes 

 were found per 10 cc. of soil throughout the year. The different species 

 do not reach their maximum and minimum at the same time, depend- 

 ing on the moisture and the temperature resistance of the organism. 

 The genera Dorylaimus, Tylenchorhynchus, Mononchus and Hoplolai- 

 mus are almost the only organisms found during the winter months. 



The class Nematoda consists of numerous small forms which are 

 usually free-living and non-parasitic. Among the free-living forms in 

 the soil, the genus Mononchus composed of numerous species 14 is 

 particularly abundant. Many of these species are cosmopolitan. 

 The Mononchs occur in all kinds of arable soil, sometimes in hundreds 

 of millions per acre. They feed on living microzoa, including other 

 nematodes. 14-16 



Among the nematodes attacking the roots of various plants, causing 

 the formation of galls, we find the sugar-beet nematode Heterodera 

 schachtii, 17 the root-knot nematode Caconema radicicola, the wheat 



13 Seidenschwartz, L. Jahreszyklus freilebender Erdnematoden einer Tiroler 

 Alpenwiese. Arb. Zool. Inst. Univ. Innsbruck, 1: 37-71. 1923. 



14 Cobb, N. A. The Mononchs, a genus of free-living predatory nematodes. 

 Soil Sci., 3: 431-486. 1917. 



15 De Man, J. G. Nouvelles recherches sur les nematodes libres terricoles. 

 M. Njhoff. Hague. 1922. 



16 See also Wiilker, G. Nematodes. Fadenwurmer. L. 11, T. 8, Schulze's 

 Biologie der Tiere Deutchlands. Borntraeger. 1924. 



17 Shaw, H. B. Control of the sugar-beet nematodes. Bur. PI. Ind., U. S. 

 Dept. Agr. Farm. Bui. 772. 1916. Baunacke, 1922 (p. 344). 



