i8o 5 . 



AN EEL WORM DISEASE OF HOPS. 



195 



upon these eelworms and Schacht's species as belonging either to the 

 genus Dorylaimus or to A nguillul a. Ultimately he named the species 

 Anguillula radicicola, and from the measurements which he gave 

 (female, 2 mm. long and -095 broad, male somewhat smaller), it is 

 evident that as late as 1872 he either did not notice or did not under- 

 stand the nature of the " cysts " in which the nematodes are met with 

 in the root-galls under observation. The difficulty of realising the 

 exact nature of the so-called "cysts" in the root-galls, even when 

 they were observed, may readily be appreciated by imagining the free 

 females of H. schachtii embedded in the hypertrophied tissue of a 

 plant. The eggs and free larvae would in such a case be easily 

 observed on cutting a section, but the dead chitinous membrane 

 forming the body of the female might be looked upon as belonging to 

 the altered tissues of the plant. The free nematodes would then be 



Fig 1. — Root-galls of cucumber plant caused by eelworms (Heterodera). 

 From the Rev. M. J. Berkeley's paper in Gardeners' Chronicle, April 7, 1855. 



classed in the ordinary Tylenchus-like groups. This mistake was made 

 by practically all the earlier observers, until the matter was cleared 

 up in 1883 by the work of Frank and Miiller ; the latter showing that 

 Greeff's Anguillula was really a Heterodera, which he named H. 

 radicicola. 



In all the papers upon Heterodera, Greeff is credited with the first 

 discovery of eelworms in root-galls of plants ; but while examining 

 the literature in connection with this subject, my attention was called 

 by Mr. Carruthers to a paper by the Rev. M. J. Berkeley in the 

 Gardeners' Chronicle of April 7, 1855, which clearly shows that this 

 view is an error. Berkeley's observations were made upon the 

 diseased roots of cucumbers nearly ten years before Greeff's dis- 

 covery, and even four years before Schacht's notice of the beet eel- 



p 2 



