626 The Insect and Allied Pests of the Hop. [nov., 



ance, and by their difference in colour from healthy ones; the 

 leaves may also curl at the edges, and become somewhat 

 spotted with the borders serrated, resembling frequently the 

 wild hop. The growth is stunted, and the bine ceases to 

 hold and falls over. The disease is known as Nettle-head, 

 and the term "skinkly " plants is sometimes applied to them. 



The cause of the disease can be ascertained by examining 

 the root fibres, when small shiny grey or brown nodules 

 will be found on them, about the size of a pin's head. It 

 will also be noticed that the delicate rootlets are thickened, 

 and many are found to be decayed. Any part of the rootlets 

 may carry the parasites. They have been found some 4 ft. 

 from the hill, and probably exist still further away, and 

 spread to the fibres of the other stocks around the infested 

 centre. 



This disease is produced by an Eelworm known as Heter- 

 odera schachtii, which also attacks beetroot and sugar beet 

 on the Continent. It has recently been reported as doing 

 considerable damage to oats in Yorkshire, and it also occurs 

 on cabbage, rape, mustard, garden cress, mangolds, charlock, 

 and couchgrass. 



The pest may easily be spread with mud on men's boots 

 and on implements, and is also said to be carried with 

 manure. As a rule it spreads but slowly, but during the last 

 three years the increase seems to have been more rapid. It 

 exists in Kent and Worcestershire, and apparently in Hamp- 

 shire. 



The life-cycle of the parasite is fairly fully known, but 

 there is still much more to be ascertained. 



The yellowish white or brown bodies on the rootlets are 

 the females, which at first lie under the rind. Afterwards 

 the rind bursts, and the lemon-shaped adult becomes exposed, 

 but retains her hold of the rootlet (see PI. III., Fig. 5). In 

 these lemon-shaped bodies we find both eggs (seen in the 

 figure) and living young, which are passed out into the soil, 

 where the former soon hatch. The young Eelworms bore 

 into a neighbouring rootlet, and there develop. Those that 

 become females gradually swell into the lemon-shaped bodies 

 referred to, and cause the rind over them to burst ; those that 

 become males mature in their old skin and then bore their 



