21. 



pots of the right size and on microplots and of 

 a relatively small number of field experiments can 

 be generalized. This is impossible for some other 

 nematodes. The reason for this is that population 

 fluctuations in these nematodes are mucn more sub- 

 ject to influences by local environental factors 

 than is generally the case in Heterodera species. 



