24 



they force their way into the younger portion of the root and imbed 

 themselves in its tissue. This irritation of the tissues of the plant 

 causes an abnormal development of the root, consisting in an 

 increased production of cells and a derangement of the tissues from 

 their natural arrangement. The worms increase in length and much 

 more in diameter, assuming a spindle and then a club shape. The 

 females continue this swelling process until they have the shajDc of 

 a gourd and a size just visible to the eye. They are now mature, 

 and having been fertilized by the male previous to their maturity 

 they produce eggs which develop into the young worms of the next 

 generation. The life period of the female is about six weeks. The 

 male worms do not remain in the swollen form, but after about four 

 weeks from entering the root they change again into a slender worm- 

 like form which enables them to move about and seek the females, 

 with which they copulate and then perish. While the worms are 

 developing, the abnormal growth of the root continues and results in 

 a gall-like swelling or enlargement and such a disarrangement of the 

 tissues that the progress of the sap through the plant is hindered to 

 an extent depending upon the number of galls on the roots. This 

 injury, together with that caused by the w^orms drawing their food 

 from the plant, checks its growth and often kills it outright or so 

 weakens it that fungous diseases come in and hasten its destruction. 



Historical Review. 



It is difficult or impossible to say just when the injurious effects 

 of nematode worms on plants were first recognized as such. It is 

 probable, however, that the first record of such injuries is that of 

 Hermann Schacht,' a German botanist, who, in 1859, in connection 

 with studies on the sugar beet, discovered what he described as " lit- 

 tle white specks of the size of a pin head," upon the roots, which he 

 correctly determined to be nematodes. Three years later Schacht 

 published again, giving a more complete description of the 

 subject of his discovery. In 187 1, Schmidt," another German, 

 made investigations upon the subject and gave to the worm discov- 

 ered by Schacht the name Heterodera Schachtii. Schmidt's work 

 was continued by several different investigators, and in 18SS 



1. Zeitschrift f. Rubenzuckerindustrie 1S59, '61, '62. 



2. Ibid 1871, 1872. 



