32. 



A stiil better method, althou,q;h it requires a iittle 

 more machinery was developed by BIJLOO (1955). The axle of 

 a small vertical motor is elongated by a rod to which a 1 cm. 

 wide and about 5 cm. long plastic cylinder is attached. The 

 cysts to be investigated are brought witn a little water in 

 a 2 cm. wiae thin walled plastic centrifuge tube after having 

 been soaked in water for some hours. Tne centrifuge tube is 

 then slid over the turning plastic rod (about 900 revs. /mm.) 

 and gently pressed against it. The cysts are now squashed 

 between the rod and the wall of the tube and the eggs are 

 rubbed apart. The whole operation takes about half a minute. 



Hatcning tests . In botn Heterodera schachti i and H. 

 rostochiensis larvae in the eggs react to substances dilfuslng 

 from the roots of host plants by hatching, wnereas in plain 

 water most larvae remain quiescent in the egg. 



The stimulating effect of root diffusates was already 

 detected by BAUMCKE (1922) but the technique of hatching 

 experiments has been worked out mainly by FEwWlCK (1950, 1951). 



The mean hatching tame is different for eggs of different 

 origin and tne individual hatching tmes are distributed more 

 or less noimally. This means that no fixed hatching times 

 should be used but tnat the experiment should be continued 

 until no material increase of the total number of larvae hatched 

 from the eggs is found anymore. 



The root diffusate. An important element in hatching tests 

 is the root diffusate, whicn should contain the chemical com- 

 pound in sufficient concentration. The only way to measure 

 this concentration is by the effect of the solution on eggs of 

 the Heterodera species, which is capable of attacking the°plant 

 from whicn the diffusate was collected. 



For the production of root diffusate plants are grown in 

 sand or soil in pots. When roots have been formed all through 

 this soil the diffusate can be extracted by saturating the 

 pots with water and collecting tne solution that drips out 

 of the pots. 



FENIVICK (1952) devised a method to compre the relative 

 concentrations of root diffusates of different origins. This 

 is done by exposing cysts to dilution series of these diffus- 

 ates. The dilxition at x^hich the number of larvae hatching 

 from the cysts does not exceed tho. number hatching in water 

 is a measure for the strength of thp hatching agent in the 

 original solution. If larval emergence is plotted against 

 log dilution a straight line is obtained. Tho intersection 



