NEMATODE DISEASE OE WHEAT. 27 
in formaldehyde of 1 : 210 strength and 4 hours and 25 minutes in 
mercuric chlorid of 1 : 1,000 strength. Submerged for 6J hours in a 
5 per cent solution of copper sulphate, 85 per cent of the larvae re- 
mained alive; and immersion for 3^ 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 Roffredi (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- 
