lo Feb., 1910.] The Potato Eel-Worm. 87 



THE POTATO EEL-WORM. 



Some Preliminary Observations showing how it differs from 

 THE Onion Eel-Worm. 



IF. Laidlaiv, B.Sc, Micro-Biologist. 



In nearly all descriptions of the Potato Eel-worm it is assumed that it 

 and the worm attacking the onion axe one and the same. They both belong 

 to ■ the Nematoda which forms a large and important sub-order of the 

 Nemathelminthes. There are a great number of species in this sub-order 

 and, although the conditions under which they live are of the most varied 

 kind, the structural differences are so slight that the determination of the 

 species is attended with great difficulty and may account for the confusion 

 that has arisen. 



Minute nematodes abound in all moist soil and around the roots of 

 plants. The great majority of these worms do not attack living plants- 

 but live in decaying organic matter in the soil. The part played by them 

 in the soil is not thoroughly understood. Sometimes they are in such 

 great numbers, that, although not distinctly parasitic, they probably do- 

 damage. Many species are free living and have received distinct specific 

 names. These, as Linstow has pointed out, may not be separate species 

 at all, but merely stages in the life history of some of th^- parasitic- 

 species. 



The eel-worms attacking plants belong mainly to the following genera of 

 the family Anguillulidse : — Tylenchns, A-phelenchus, and Heterodera. They 

 are of small size and are provided with a spine or spear which works to and' 

 fro through the mouth, and by which the worm bores into the tissues of a 

 plant. The onion worm is larger than the potato worm, averaging one- 

 twentieth of an inch in length, while the potato worm averages only 

 one-fiftieth of an inch. The reverse is the case with the newly-escaped 

 embryo, that of the potato worm being the longer. The eggs, also, of the 

 potato worm are larger than those of the onion worm. 



If we take a potato that is affected with eel-worm, we will find rounded 

 swellings on the surface; these may occur all over the potato or in patches. 

 The swellings vary in size and are often confused with scab. (Eel-worms 

 are frequently found in scabby potatoes, there being a double infection.) 

 If we take a potato showing these swellings and cut it into thin slices at 

 right angles to the surface, we will see under the skin at distances varying 

 from 1-32 to \ of an inch, rarely deeper, little round cysts 

 which are visible to the naked eye, being about the size of the head of a 

 very small pin ; these are the female worms which have become distended 

 with eggs. In a potato that is newly dug, the little cysts are transparent 

 and very difficult to make out with the naked eye, but in one that has 

 been kept for some time they are more easily seen as the cyst becomes 

 opaque and nearly white in appearance, and by-and-bye the starch cells 

 in the neighbourhood become brownish through degeneration. This is 

 analogous, no doubt, to the degeneration which takes place around the 

 cystic form of some of the nematodes affecting animals. After the female 

 has assumed the rounded form it dies. In the case of a worm that has 

 only recently assumed this rounded or cystic form, on expressing the con- 

 tents and examining under a low power, we find the cyst contains only a 

 mass of germinal cells, while in an older cyst these are contained in a 

 limiting tube-like membrane, probably the wall of the uterus itself which 



