488 
Journal of Agricultural Research 
‘ Vol. XXV, No. 12 
OVERWINTERING AND DISSEMINATION 
No experimental evidence on the overwintering and dissemination 
of Bacterium trifoliorum is at hand. The field observations, however, 
during the several seasons in which the disease has been investigated 
show that it recurs annually in the same general areas in the clover 
fields and on the same small groups of plants in meadows and lawns. 
One old clover field at Madison was observed almost daily during April, 
May, and June, 1920. The disease appeared, with the advent of warm 
weather in April, upon the young leaves soon after they had unfolded. 
Here, no doubt, fallen diseased leaves harbored the parasite during 
winter and it spread from them to the new leaves. The disease was 
very much in evidence during May, and by blossoming time every leaf 
on a plant might be conspicuously spotted. i 
Fig. 3 .—Diagram of two clover leaves in which insect injuries {Phytonomus punctalus) and the bacterial 
lesions ( Bacterium trifoliorum ) are associated. In the leaf at the left, the lesions were young and water- 
soaked and apparently had originated at the insect puncture. In the leaf at the right, the insects may, 
at least in some places, have eaten out the invaded tissue. In any case, the water-soaked margins indi¬ 
cated that the invasion was still progressing. (Drawing by Charles Drechsler.) 
The fact that the disease under favorable conditions involves the 
plant so generally makes it highly probable that the floral parts might 
become infected. Lesions have not been observed, however, on the 
floral organs, but they are of common occurrence on the flower pedicels. 
Even though flowers are not involved, there would be ample opportunity 
for the seed to become contaminated either while yet in the field or during 
harvesting or threshing. The initial infections in newly planted fields 
could thus come from contaminated seed. That seed serves as the 
primary source of infection is indicated by the occurrence of diseased 
plants in newly planted pastures and lawns. Should this disease ever 
become seriously destructive, any precautionary measures looking 
toward its control or prevention, especially in new plantings, should 
stress the possible value of seed disinfection. 
