NEMATODE DISEASE OF WHEAT. 27 



in formaldehyde of 1 : 240 strength and 4 hours and 25 minutes in 

 mercuric chlorid of 1 : 1,000 strength. Submerged for 6^ hours in a 

 5 per cent solution of copper sulphate, 85 per cent of the larvae re- 

 mained alive; and immersion for 3 J hours in sulphuric acid of 0.5 

 per cent strength failed to kill 60 per cent of them. These few 

 figures are sufficient to indicate the impracticability of using these 

 chemicals for disinfecting seed. 



By comparing the figures in Table IV with those in Table V it 

 will be seen that a considerably longer time was required for the 

 chemicals to kill the larvae when they were inclosed in galls than 

 when they were not. 



OVERWINTERING OF THE PARASITES. 



It is in the second larval stage that the organism lives from one 

 season to the next. But just where most of these larvae overwinter 

 outside is an unsettled question about which there is no uniformity 

 of opinion among the investigators who have studied the problem. 

 Some of the earlier investigators, including Eoffredi (30) and Hens- 

 low (16), were of the opinion that the larvae overwintered in the 

 protective galls which shattered out of the wheat heads at harvest 

 time and dropped to the ground or else during the fall were sown 

 in the soil along with the seed. According to these earlier workers 

 the larvae did not escape from the galls into the soil and infect the 

 wheat plants until spring. On the other hand, Davaine (11) in 1857 

 concluded from his experiments that infection takes place in the fall 

 when the nematodes are freed from the galls and that the larvae over- 

 winter in the young wheat plants. Since that time this view had 

 been generally held by scientific workers until 1909, when Marcinow- 

 ski (22) deduced from rather extensive experiments that most of the 

 larvae remain in the galls throughout the winter, although a few may 

 escape at almost any time during the fall or winter and either live 

 free in the soil or locate in the seedlings. It will thus be seen that 

 there is. no general agreement as to the manner in which the parasite 

 passes the winter in the field. 



The writer has tentatively concluded from preliminary observa- 

 tions on field experiments which are still under way that most of the 

 larvae get out of the galls in the fall and overwinter either in a free 

 state in the soil or as an ectoparasite in the seedlings. Evidence sup- 

 porting this view was found in January, 1919, when- a large number 

 of nematode-infected seedlings were observed in an experimental 

 field plat. These infected seedlings occurred in rows of wheat which 

 were grown from wheat seed planted October 11, 1918, in uninfested 

 soil. Sown along with the seed was an equal volume of unopened 

 nematode galls. It seems probable, therefore, from the large num- 



