THE ROOT-KNOT EELWORM. 5 



characteristic knots on the roots, a later microscopic exami- 

 nation of which showed that these contained numerous eelworms. 



Beyond the marrows, cucumbers were affected in a similar 

 manner. 



The measures adopted in this case were as follows : The 

 plants were all taken up, saturated with paraffin, and burnt on 

 the ground, which was then liberally treated with gas lime. 



In other countries species of Heterodera are known to infest 

 wheat, barley, beet, cabbage, radish, and turnip crops : while 

 there are few plants which allied species will not attack. 



It would seem that the knots are not always present, for Mr. 

 \Ynrburton mentions in the case of the swedes examined by him, 

 that " the root was small and ill-formed, but the most striking 

 characteristic was the remarkable out-growth of side roots, which 

 presented a dense mass of fibres. These were not knotted or 

 swollen, but were found on microscopic examination to be crowded 

 with the worms." 



LIFE-HISTORY. 



Heterodera belongs to a group of minute worms, which are 

 mostly very small, and usually free-living, being found in decaying 

 vegetable matter in water, or in living plants. A familiar example 

 of this group is The Stem Eelworm (7 'ylenchus devastatrix, Knhn). 



The larva by means of a needle-like process bores into the deli- 

 cate rootlets of the plant, and after burying itself in the tissues 

 becomes stationary. If a male, it then commences to swell, shrink- 

 ing within its skin, at the same time the rootlets become irregular 

 in shape and the so-called knots form (Fig. I, A and B). 

 Ultimately a much longer worm is formed within the old skin, 

 which is now little more than a protective sac, the worm then 

 pierces the sac and bores its way through the tissues of the 

 root and becomes free. 



The female does not undergo any like change in the root, but 

 after a time ilso leaves it and becomes attached to the surface of 

 the root, here it is fertilised by the male, and then undergoes 

 considerable degeneration. Ultimately it becomes a brood 

 pouch full of ova and larvae. Most of the ova hatch out into 

 larvae within the body of the parent, which then drops off the 

 root and dies. Three hundred to three hundred and fifty eggs are 

 produced at a time, and there are six or seven generations in a 

 year. 



PREVENTIVE AND REMEDIAL MEASURES. 



Great care should be taken in seeing that all diseased tomato 

 or cucumber plants are burnt, and the soil in which they grew 

 should be liberally treated with gas lime. 



Saturating the soil three times at intervals of a fortnight, 

 with one part of carbolic acid in twenty parts of water, is also 

 said to be effective. 



