64 



Resume. 



Nematodes are small, mostly microscopic worms allied to the 

 earth worm ; many are entirely harmless, some are parasitic in ani- 

 mals, and a few in plants. Of the many species occurring in this 

 section only one is known to damage plants. This is called Hetero- 

 dera radicola and is the cause of the so-called " root-knot " disease 

 of many plants. The species is very similar to and perhaps iden- 

 tical with the European H. Schachtii which causes so much damage 

 to the sugar beet. 



The amount of damage caused by nematodes to economic plants 

 throughout the world is quite large. 



The number of families and species of plants subject to nematodes 

 are numerous. They not only attack the roots but frequently other 

 parts of plants as well. 



Certain species of nematodes, Tylenchus, etc., are indigenous to 

 our climate and by means of their resistant eggs they are capable of 

 surviving our winters, but the parasitic species Heterodera cannot. 



The greatest amount of injury done to plants in the Northern U. 

 S. is largely confined to greenhouses and occurs to such plants as 

 the cucumber, tomato, violet, rose, cyclamen, etc. which are affected 

 in their 'roots. Not infrequently, however, outdoor plants are subject 

 to nematodes by being brought in contact with infested earth or 

 manure. 



Plants affected by Heterodera usually appear sickly and gradually 

 fade away and die. The roots of such plants are found to be more 

 or less covered with various sized galls or swellings. These galls 

 are the result of an abnormal growth of the root due to the young 

 worms forcing their way into it, and there remaining to complete 

 their development. The damage to the plant is not due to the feed- 

 ing of the worms upon the roots, but rather to the fact that the flow 

 of sap from the root is cut off by the abnormal development of the 

 tissues. 



The nature of the problem of nematode control is one which must 

 be based upon a knowledge of the life history and environmental 

 conditions affecting the organism. 



It has been found that the use of chemicals is of no practical 

 value. None of the chemicals which we have used are capable of 

 killing the eggs of nematodes when confined in the soil, and unless 

 this is accomplished the treatment is of no account. 



