'324 ECONOMIC IMPOKTANCE OF ^•EMATODES. 



" lady-finger " banana, etc.; many oi-namental slirubs 

 and flowers, such as carnation, rose, violet, snapdragon, 

 etc. ; numerous vegetable crops, sucli as carrots, turnips, 

 cabbages, potatoes, tomatoes; cereals, sucli as oats, 

 wheat (Triticvjii aestivuin), and perhaps maize, and 

 other plants such as tea, coffee, tobacco, cotton, flax, 

 okra, lucerne, rubber tree, elm, sugar cane, together 

 with many others, are more or less seriously damaged. 



I Remarks on the life-history of Heferodera, as investigated 

 by me in South Africa, will be found on page 330. 



Tylenchvs acutocaudaf us . — The causative agent of 

 a disease in banana groves recently reported from the 

 vicinity of Alexandria. The same parasite has also been 

 found in coffee trees. 



T . hiforinis. — A parasite of the roots of sugar cane. 

 Reported from Haw^aii. 



T . devastatri.T, syn. : T . dtpsaci, T. scandens. — 

 This is the common stem eel-w^orm widely distributed 

 over Europe, Australia and other countries. It is 

 responsible for much damage to onions, narcissus bulbs 

 ' and buckwheat. It produces ,stem rot in clover. In 



South Africa, although only of recent introduction, it 

 has become widespread, and makes the cultivation of 

 lucerne almost impossible in many districts. When 

 once introduced, its eradication has, so far, proved 

 impossible. 



T. oryzae. — Infests rice plants in Java {? = T. 

 angusta, a rice plant parasite of Bengal.) 



T. mahoganii. — A parasitic Nematode connected 

 with a disease in the mahogany tree. 



T. penetrans. — First described from the roots of 

 violets in New York (1911). It has since been recorded 

 from potatoes, cotton, and camphor tree roots. 



T . sem.ipenetrans.-—K. parasite of the roots of citrus 

 plants in California, Algeria, Australia, etc. 



T. similis. — ^A parasite described by Cobb (1915), 

 in the roots of sugar cane and banana. 



T. sacchari. — ^The probable cause of a sugar cane 

 disease known as " sereh." 



T. tritici.- — ^Causes a pernicious disease of wheat, 



producing " ear-cockles." "Widespread in Europe and 



America. 



Besides the direct damage inflicted by Nematodes, as 



plant parasites, a much wider role has been assigned to them 



in the production of disease. Not infrequently their presence 



in the roots permits the invasion of malignant bacteria and 



other pathogenic organisms, which are the primary causes of 



disease. An example of a bacterial disease of cotton roots, 



made possible by the ravages of. Nematodes, is found in the 



" black-root " disease in America. 



