ROOT-KNOT EELWORM. 137 



Although there are some pomts of great similarity between Eel- 

 worms of the genus Heterodera and Tijlenchus, they are clearly distin- 

 guishable with the help of good microscopic powers, if the females are 

 present, for whilst both males and females, and also the larvae of the 

 Tylenchus devastatrix, are thread-like, or like long and narrow eels in 

 miniature ; in the case of the Heterodera radicicola it is only the males 

 and the larvae in their early stage which have this thread-like or eel- 

 like form ; the females are of the peculiar form, like a gourd, swelled 

 at the lower part, and contracted at the top, which is figured at p. 127. 



This is a matter of considerable practical importance, for the treat- 

 ment of the two kinds of Eelworms by no means rests on the same 

 basis. The Tylenchus may be destroyed, and the plants brought over 

 attack, by cheap and easily applied chemical dressings, which so far as 

 we see at present are useless for extirpation of Heterodera radicicola. 



Careful experiments, on what is, unfortunately, necessarily a large 

 scale, are now in progress, of which any satisfactory results will be 

 recorded.* 



* For those who wish to study the subject at length, I may mention that of the 

 papers which I have quoted from, that by Prof. Geo. F. Atkinson deals at minute 

 length, and very serviceably for scientific observers, with the structural charac- 

 teristics and life-history of the Nematodes. It also gives many excellent and enor- 

 mously magnified figures of them in both sexes and various stages, with anatomical 

 detail; and, in addition to collateral considerations, most copious references are 

 given to publications on this and other allied Nematode attacks, and somewhat 

 analogous gall formations, by many European, and also some American writers. 



The paper by Dr. Neal deals chiefly with the subject practically, from the horti- 

 cultural point of view, as the " Eoot-knot Disease" of Florida, by an Anguillula, 

 which, in the absence of the literature of the subject, was named by the writer the 

 Anguillula arenaria. This paper also has many plates, including some very useful 

 coloured figures of galls. 



