PLATE s 
Colonies of the clover organism. 
Potato agar plate colonies of Bacterium trifoliorum incubated for 9 days at 26° C. 
A. —Wisconsin isolation 1916-II, enlarged showing circular surface colonies 
and lens-shaped deep colonies. Note the rugose umbonate centers with radial cor¬ 
rugations extending outward toward the plain marginal zone. In very slow-growing 
colonies, these radial corrugations are commonly crossed by concentric folds. The 
plain zone at the margin is commonly raised, although less pronounced in some cases, 
as shown in B. 
B. —Wisconsin isolation 1920-III enlargedX*>3• The same colony characteristics 
appear in this strain as in 1916-II and other slower growing isolations. Indeed, the 
amount of growth may not be much greater, for the colonies seem more spreading and 
relatively thinner. Note, for example, the absence in colony B of the raised edge 
which is found in those of A. If this strain had not evidenced this spreading charac¬ 
teristic so constantly both in plates and tubes (PI. 6) of the different agars used, it would 
seem to be an accident of moisture content. In their reactions in milk, sugar media, 
etc., the two strains, 1916-II (A) and 1920-III (B), seem identical; therefore these 
differences are attributed to variations in growth vigor and other minor or transient 
characters. 
