28 BULLETIN 842, U. S. DEPARTMENT OF AGRICULTURE. 



ber of seedlings infected and from the many parasites found in some 

 of the plants, that most of the larvae must have escaped from the galls 

 before January. It is not safe, however, to draw general conclusions 

 from such limited observations, and the manner in which the larvae 

 live through the winter may depend upon the seasonal conditions 

 occurring in the fall. Most likely the nematodes are liberated from 

 the galls when favorable moisture and temperature conditions exist, 

 regardless of whether this be in the fall, winter, or spring. That the 

 larvae, either within or without the gall, may withstand extreme cold 

 is indicated by the laboratory experiments of Davaine (11) , who sub- 

 jected them without injury to a temperature of 15° to 18° C. below 

 zero for five hours. The writer has kept them embedded in ice for 

 several days and on reactivating them in water observed no in- 

 jurious effect of the treatment. Indeed, the larvae began their move- 

 ments while the water was barely above the freezing point. 



HOST PLANTS. 



Investigators disagree as to the host range of Tylenchus tritici. 

 Most of them, however, maintain that it is a highly specialized 

 parasite normally attacking, to any appreciable extent, only wheat. 



Both Roffredi (30) and Marcinowski (22) were able to produce 

 only small, imperfect flower galls of barley (Hordeum vulgar e) 

 and rye (Secale cereale) by artificial inoculation with larvae. In a 

 similar manner more pronounced infection was secured in spelt 

 (Triticum spelta), although in this plant the number and size of 

 the galls fell much below that of wheat {Triticum vulgare) sub- 

 jected to like treatment. Also, under natural conditions, spelt is 

 reported to have been slightly diseased. Henslow (16), without 

 adducing convincing evidence, states that he obtained with diffi- 

 culty a slight infection of oats (Avena sativa), rye, and barley. 



During the season of 1918-19, the writer, in cooperation with 

 A. G. Johnson and R. W. Leukel (9), induced an abundant infec- 

 tion of emmer (Triticum dicoccum) , rye, and spelt, and a shght in- 

 fection of oats. These crops were grown in a previously unin- 

 fested field and were inoculated by sowing in certain rows seed 

 mixed with nematode-containing galls. In other rows seed in- 

 fested with free nematodes was planted. 



In the case of rye, spelt, and emmer, flower galls of about the 

 size of those produced on wheat occurred on numerous spikes of 

 these plants. In oats only a few small flower galls were found in 

 a limited number of plants. Similar experiments on barley gave 

 only negative results. 



Thus, from the rather limited data available on the subject it is 

 evident that the nematode may parasitize cereal grasses other than 



