Populf6 



('viable cysts'), Figiire 3 (Jones 19U5); and here there is a strong 

 correlation with numbers of eggs. 



Figure 2 



50- 



20 40 60 80 100 120 )« 160 180 200 220 

 Mean number of cy»ts (soog. of soil in lo lots of 50g.) 

 Poisson tests ; the values of x' associated with cyst counts of the 

 various fields for the year 1937. 



Figure 3 



10 2P 30 40 50 60 70 80 90 100 ■ 110 

 Mean number of viable cysts (500 g. of soil in 

 10 low of so g.) 



tests; the values of x' associated with viable cyst counts 

 of the various fields for the yea» 



Numbers of cysts, with contents, is the measure usually employed in 

 advisory work, and it is often coupled with some arbitrary standard 

 of fullness (e.g. Triffitt 193U). These arbitrary standards may 

 introduce errors of a personal nature, and, in any case, render it 

 difficult to relate the results of different groups of workers. 

 Petherbridge (1938) and Oostenbrink (1950) crushed cysts under a 

 cover glass and estimated the 'halos' of eggs surrounding the ruptiu-ed 

 cysts. Such methods give variable results that are generally much too 

 low. A better method is to make up the liberated eggs (and larvae) 

 into a suspension from which an aliquot may be withdrawn and counted. 

 The estimation of alicuots from a bulk suspension presents the same 



