R. S. DUNHAM 201 



sprayed when flower development is active. Thus the boot and heading 

 stage of small grains, the bud and bloom stage of flax, and the tasseling 

 stage of corn have been singled out as particularly susceptible periods. 

 It is questionable whether rapidity of growth or development is very 

 closely associated with susceptibility in these stages. It is quite probable 

 that spraying at these times affects the flower development so that the 

 injury is directly expressed in yield of seed. 



Morphological responses of plants to 2,^-D. — The reaction of crop 

 plants sprayed with 2,4-D is often characteristic. Morphological changes 

 as described in the literature are as follows: 



Wheat exhibits club-shaped spikes, irregular arrangement of 

 spikelets, branched rachis, 2 spikelets per rachis node, fused 

 glumes, thickened culm, and chlorosis. (See 20,21,32,42). 

 Oats show onion leaf, blasted spikelets, late tillering, and 

 interference with heading. (See 8,23,44). 

 Barlev shows extended internodes on rachis, round inter- 

 nodes, 2, 3, or more kernels at each rachis node in 2-row 

 varieties, naked kernels, multiple awns, spikelet groups in 

 2-row resembling 6-row type (i). 



Flax shows bending and twisting of stem, twin bolls, fused 

 leaves, swollen stems, excessive branching, death of the cen- 

 tral stem, and chlorosis. (See 16,45). 



Corn shows stalk curvature, stalk brittleness, lodging, fascia- 

 tion of brace roots, and onion leaf (See 6,7,22,31,43). 



These abnormalities are not necessarily permanent. Frequently plants 

 recover from them with no detrimental eff'ect on yield (6,7,25,36,44,45). 

 Delay in maturity, and reduction in height are commonly mentioned 

 in the literature as eff"ects of 2,4-D application. Tandon (45) points 

 out that the delay in maturity of sprayed flax is greater at the final 

 bloom stage than when ripe and that at practical rates of application 

 this delay in maturity "is not of much practical consequence since 

 the sprayed flax was not more than 2 days later than the check." 

 Commenting on the frequent reports of serious delay in flax, Dunham 

 has pointed out that two possible explanations for these contradictory 

 results cannot be tested because of insufficient pertinent information in 

 the reports submitted. Delay as reported may have been measured at 

 bloom, rather than at maturity. Flax ripening too late in the season 



