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



In examining many of the common grasses, especially Bromus 

 secalinus and Dactylis glomerata, growing in and near severely dis- 

 eased fields of wheat in Virginia, the writer has been unable to find 

 nematode galls of either the flower or leaf. The evidence at hand, 

 therefore, seems to indicate that the nematode on wheat is not iden- 

 tical with forms producing flower galls on wild grasses. 



Not infrequently nematode galls located only on the leaves of 

 grasses have been reported. Some of these are caused by organisms 

 morphologically similar to and by some investigators also thought to 

 be identical with Tylenchus tritici. The writer has found such leaf 

 infections particularly abundant on C'alamagrostis canadensis in 

 Wisconsin, but these are caused by a species of Tylenchus different 

 morphologically from the wheat nematode. In general appearance 

 they resemble somewhat the uredinia of certain rusts, for which 

 they have been mistaken. As a rule, they are small, yellow, ellip- 

 soid swellings, about 5 mm. long, 2 mm. wide, and 2 mm. thick, which 

 involve the entire thickness of the leaf at the affected point, causing 

 it to protrude slightly from the upper and lower surfaces. Their 

 long axis extends in a direction parallel to the midrib, and they may 

 occur on any portion of the leaf. Grasses so affected have been ob- 

 served many times in both America and Europe. As in the case of 

 the nematodes causing flower galls on various grasses, it is not pos- 

 sible, on account of the brevity of descriptions, to determine posi- 

 tively whether all the nematodes in the leaf galls of grasses differ 

 from Tylenchus tritici. On the whole,, it seems rather unlikely that 

 any of them are identical with the wheat organism, since the latter 

 is primarily a parasite of the inflorescence and only occasionally pro- 

 duces leaf galls. 



An interesting and important question is whether identical or- 

 ganisms are responsible for the leaf and the flower galls of the wild 

 grasses, on some of which both types of attack occur. In the case 

 of wheat, the writer has shown that the two kinds of galls may be 

 induced by Tylenchus tritici. Davaine (11) obtained similar results 

 and Kieffer (20) also noted definite leaf swellings which contained a 

 species of Tylenchus very likely identical with T . tritici, but Marci- 

 nowski (22) was unable to find leaf galls on wheat. 



From what has been said it is evident that considerable investiga- 

 tion is needed to extend our knowledge of the relation between 

 Tylenchus tritici and other nematodes occurring on grasses. 



METHODS OF SPREADING THE PARASITES. 



Only in its second larval stage does the parasite constitute a source 

 of new infection. All other stages of the life cycle are more or less 

 transitory, unable to withstand unfavorable conditions, and unable 

 to live or develop for any appreciable time outside the host plant. 



