T. GOODKY 21 



recently given accoiint.s of the serious damage to red i/lover in certaiii 

 areas of the norbh-west States in the United States of America due to 

 Ti/lenchus dipsaci. 



A detailed investigation of the parasitism of Tylenvhu.s dipsaci seemed 

 highly desirable, and as a beginning the question of the susceptibiUty of 

 a number of clovers and other legumes to attack from the worm was 

 taken up. 



In the following pages, which arc to be looked upon as a preliminary 

 communication only, an account is given of the attempt which I have 

 made to obtain a numerical expression of susceptibiHty and arrive at 

 some figure which may be considered as an index of susccptibiliti/ for a 

 given kind of clover or other host plant. 



The investigation was undertaken in 1920 when I was acting as 

 lielminthologist on the staff of the Institute of Plant Pathology at the 

 Rothamsted Experimental Station, Harpenden, whilst some of the 

 material has been worked up since I was transferred to this laboratory. 



I wish to acknowledge my indebtedness to Mr R. A. Fisher of the 

 Rothamsted Laboratory for kindly working out the Standard Error in 

 connection with the percentages of deformed seedUngs, and for some 

 suggestions. My best thanks are also due to Mr Arthur Amos who helped 

 me by supplying diseased clover plants and to Messrs Sutton & Sons 

 who very kindly sent the seeds used in these experiments. 



THE PARASITE. 



The parasite causing the disease is a small nematode worm belonging 

 to the family AnguiUulidnc. popularly known as eelworms. It is not 

 my intention in the present paper to give a detailed description of the 

 worm; this has been done by many previous investigators whose works 

 may be consulted: good accounts of it are to be found in Ritzema-Bos 

 (1892) and Marcinowski (1909). 



The adults are visible to the naked eye when seen suitably illuminated, 

 and measure from one milhmetre to one and three-quarter millimetres in 

 length. The widest part of the body is about one-fortieth of the total 

 length. 



The sexes are distinct and the males are on the whole a little shorter 

 and narrower than the females. Although, as stated above, the worm lias 

 been described many times previously, there is still need for much 

 information concerning the structure of several of its organs. Moreover, 

 we need to know exactly how the parasite gains access into the tissues 

 of the host plant, and also how it uses the chitinous stylet which it carries 



