ECONOMIC IMrORTANCE OF NEMATODES. 33S 



remains to be done in the interests of applied science. Especi- 

 ally do the free-living- and plant parasitic genera require 

 immediate attention, but it can only be a matter of time noAv 

 before the ravages caused by " eel-wonns " to the majority 

 of our crops will compel their closer investigation. A slight 

 conception of the enormous losses to agriculture inflicted by 

 some of the better known Nematode plant parasites may be 

 obtained from the following brief considerations : — 



Heterodera radicicola, the parasite causing root-galls, or 

 root-knot, is perhaps the most serious of Nematode crop pests. 

 It infests over 500 species of plants, more than half of which 

 number are of economic value. The actual monetary loss to 

 farmers, due to this parasite, is inestimable. Cobb states that 

 the losses would amount to a fortune for a nation. The parasite 

 has a world-wide distribution, and certain localities are some- 

 times so badly infested as to make agriculture impossible. So 

 far, no effective remedy, whicli can be satisfactorily applied 

 on a large scale, has been devised. 



H. .<^e]iac]itii, the European sugar-beet parasite, makes beet 

 cultivation impossible in heavily infected fields. When only 

 slightly infected, a loss of one-third of the entire crop is not 

 uncommon. 



TylencJms tritici, the cause of " ear-cockles " in wheat, 

 not only decreases and depreciatesi the yield of grain, but 

 during its sojourn in the tissues seriously handicaps the growtli 

 of the plant. This Nematode disease lias proved in some cases 

 to be one of the most destructive diseases to whicli wheat is 

 subject, often causing losses to the extent of 25 to 50 per cent, 

 of the crop value. 



T. devastatrid-, as its name implies, is a most destructive 

 organism, causing much damage to hyacinth bulbs, onions, 

 buckwheat, etc. It is of comparatively recent introduction 

 into South Africa, and already makes the cultivation of lucerne 

 impossible in many districts. So far, its eradication has not 

 been effected. The ravages of this Nematode on lucerne, the 

 principal food of the ostricli, and the losses caused by 

 Trichostronfiylus douglasi, the Nematode parasite of ostriches, 

 threatened at one time to ruin tlie iiidustiy in certain parts of 

 the Cape Colony. 



The destructive activities of Nematode parasites among 

 stock and other domestic animals are too well known to require 

 repetition. 



As regards the Nematode parasites of man. it is often 

 apparent that their distribution is more or less localised. South 

 Africa is happily free from many of those pests which are 

 prevalent in adjoining territories, but it is also seen that the 

 physical and other conditions, which would allow of the 

 flourishing of some of these parasites if once introduced, are 

 often present in this country. A potential danger thus exists, 

 and an adequate knowledge of the life-history and bionomics 

 is necessary to prevent the introdiiction of the parasites. In 

 the same way it is evident that in dealing- with microscopic 



