ECOXOMIC IMPORTANCE OF NEMATODES. 323 



111 order to point out more prominentlj- the role played by 

 the Nematodes as parasites of great economic importance, the 

 following' list has been prepared. It is hoped that it may help 

 to supply a want felt by zoologists in South Africa for a general 

 list of Nematode parasites. For the sake of convenience the 

 subject has been treated under three main heads, according- to 

 the hosts affected — agricultural crops, domestic animals, 

 and man. 



Some remarks are also appended (Section IV.) on the 

 author's researches on the life-history of Heterodera in South 

 Africa. 



I. — Some Nematodes of Agricultural Importance. 



Almost without exception, the Nematodes, or " eel- 

 worms," that parasitise the tissues of plants, belong to the 

 family Anguillulidae, while the genera mainly concerned are 

 AphelencJius, Heterodera and TylencJufs. Yery few plants 

 are totally immune to the ravages of one or other species of 

 these genera, and the tissues infested, although often localised, 

 may vary from the roots to parts of the stem, vascular tissues 

 of the leaves, etc. The genera AphelencJuts, Heterodera and 

 Tylenchus are characterised by the presence of a buccal spear, 

 a chitiiious organ, which enables them to pierce the root tissues 

 in order to carry on their parasitic life effectively. 



Of special importance are the following:- — 



AphelencJius armerodus .—A parasite on violet buds. 

 A. cocopJiilus. — The cause of serious maladies in 

 the coco-nut palms in the West Indies. 



A. pyri. — A remarkable parasite which causes pears 

 to decay. 



A. fragaria. — A destructive strawberry parasite. 



Heterodera schachtn. — It was probably due to the 

 ravages of this organism that the attention of observers 

 such as Schacht, in 1859, and Schmidt, in 1871, was 

 first drawn to the importance of Nematodes as serious 

 plant pests. H. schachtii was demonstrated to be the 

 direct cause of " sugar beet sickness " in Germany and 

 many other European countries. The same parasite has 

 since been found to form galls, or root swellings, on 

 maize, barley, rye, oats, winter and spring wheat. In 

 hops it causes the disease known as " nettle-head." 



Heterodera radicicola. — 'This is without doubt the 

 most troublesome of Nematode plant parasites. The 

 roots of the plant are attacked by the larval worms, and 

 large disfiguring galls, or root-knots, are produced, 

 which usually interfere with and upset the vital func- 

 tions of the roots. More than 500 plants, the majority 

 of which are of economic value, are attacked by this 

 parasite. Among the more important host plants are: 

 Most orchard trees, such as peach, apple, g'rape, fig, 



