36 



nematodes but we have no data in regard to this method when car- 

 ried on upon a large scale. We have, on the basis of our own ex- 

 periments, frequently advised cucumber growers who were troubled 

 with nematodes, to try this method on a more extensive scale than we 

 covild. But as yet we have received no reports. Most of our 

 cucumber houses lie idle long enough during the summer to give this 

 method a more thorough trial than is possible out of doors, inasmuch 

 as greenhouse soil is not subject to occasional drenchings from rain 

 and consequently the drying can be carried on to a much greater 

 extent. This treatment is so simple that it is hoped reliable data 

 may be furnished ere long. 



(c). THE HALLE OR CATCH CROP METHOD OF DESTROYING NEMATODES. 



The method of treating nematodes other than by chemicals was 

 originated and employed some years ago by Dr. Julius Kiihn of the 

 University of Halle, Germany, and it has since been extensively test- 

 ed by Dr. Kiihn and his colleague Dr. Hollrung, both of whom have 

 spent some years in investigating the nematode pest in connection 

 with the sugar beet industry. In 1896 we visited Halle and exam- 

 ined the work done at this institute, and we wish here to express to 

 Dr. Max Hollrung our appreciation of the many courtesies shown us 

 while there. 



The parasitic nematode (Heterodera) is widely distributed and 

 very injurious to the sugar beet in Europe and any method which 

 endeavors to control it must be one which can be applied cheaply, on 

 account of the large area which it is necessary to treat. The meth- 

 od employed is based upon the knowledge gained from a study of 

 the life history of the organism. It has been shown by Strubell that 

 the worm on entering the beet develops its young in the course of 

 six weeks, and Kiihn taking advantage of these facts reasoned that, if 

 the infested host plants could be dug up and destroyed before the 

 worms laid their eggs, the soil could be rid of a large number of 

 worms. His method, therefore, consists in trapping the worm and is 

 popularly known as " The Catch-crop Method ", and for the succes- 

 ful carrying out of this idea in treatment he made use of a host plant 

 especially susceptible to Heterodera, generally a species of mustard 

 (Brassica Rapa rapifera, Metzg.) which he sows on the soil in the 

 spring. The nematode attacks the mustard, gains entrance to the 

 root, and locally stimulates the plants to produce galls. About the 



