14 BULLETIN 842, IT. S. DEPARTMENT OE AGRICULTURE. 



the same degree of development, become externally desiccated, mo- 

 tionless, and partly coiled. In this condition they are capable of 

 remaining dormant for many years. The writer has recently reac- 

 tivated in water such larvae from galls which had been imported 

 along with wheat from Turkestan in 1910. According to Needham 

 (26), a "M. Baher " in 1771 secured vital movement in specimens 

 which the former had sent him 27 years previously, in 1744. During 

 this period the larvae had been kept in protective galls in the labora- 

 tory. When mature galls previously soaked in water are opened, 

 the larvae upon being freed immediately straighten out with a 

 mechanical movement and later, sometimes within a half hour or 

 occasionally only after a day or more, begin their sluggish eellike 

 vital motions. The two types of movements, though distinctly dif- 

 ferent and due to different causes, have nevertheless been confused 

 even by trained observers. Dead larvae may show the former — that 

 is, the mechanical straightening — in a manner very similar to live 

 ones, but only living larvae show the vital, eellike movements. Very 

 probably, however, "M. Baher" in observing the 27-year-old ma- 

 terial referred to above saw both the mechanical and vital move- 

 ments. 



Moistened or submerged in water the larvae move actively (PL V, 

 B), but not in the rapid manner so typical of free-living forms. 

 After being held in distilled water at room temperature for more 

 than two months, the writer has observed them still sluggishly mov- 

 ing. During this time the only change noticeable was in transpar- 

 ency, caused undoubtedly by the utilization of reserve food. The 

 translucency increased with the length of time of immersion until 

 finally, at the last observation, they were almost transparent. Liber- 

 ated in soil under natural conditions, they are capable of living in a 

 free state much longer. Marcinowski (22) concluded from care- 

 fully conducted experiments that they could probably live thus in 

 an active condition for seven months or more. In the application 

 of control measures for the wheat nematode, as for the root-knot 

 nematode (Heterodera radicicola), use can be made of the fact that 

 these active larvae will starve to death in a comparatively short 

 period. 



Although capable of living free in the soil or elsewhere for several 

 months, the larvae undergo no development until the host plant is 

 penetrated. By their own eellike locomotion they travel through the 

 soil in search of wheat seedlings, and numerous larvae finally become 

 located between and within the leaf sheaths near the apical growing 

 points of the culms. They may use the roots as a means of elevating 

 themselves to other parts of the host, but, contrary to what Rof- 

 fredi (30) and other investigators thought, do not normally penetrate 



