464 
Journal of Agricultural Research voi. xxvii, no. 7 
ready ingress of the water necessary for germination of the spore. 
Without the action of the stimulatory materials, germination in distilled 
water either is delayed or may not occur at all. The exact nature of the 
action of these substances on the spores is not known. However, they 
all have the common property of reducing the surface tension of water. 
Larson (24) has shown that the surface tension of the medium may 
have a very definite effect on the cultural habit of certain bacteria. 
Pellicle-forming bacteria, such as those of the Bacillus tuberculosis and B. 
subtilis groups, which habitually grow upon the surface of liquid media, 
will grow throughout the body of the medium when the surface tension 
is reduced from 59 dynes (the S. T. of ordinary broth) to from 40 to 45 
dynes. The suggestion is made that the bacteria grow throughout the 
medium when they are properly “wetted.” 
In a later paper Larson and Montank (25) observe that the patho¬ 
genicity and viability of the tubercle bacillus also are affected by the 
reduction of the surface tension of the medium. They suggest that 
“when the tubercle bacilli are growing diffusely throughout the medium 
they are wetted and, therefore, when introduced into the animal body, 
are penetrated by the antibodies or bactericidal substances present and 
destroyed.” 
The viability of these organisms is thus dependent on their degree of 
permeability to bactericidal substances, and this permeability is corre¬ 
lated with a reduced surface tension of the medium. 
It has been considered that changes in surface tension of the medium 
sometimes affect the germination of fungous spores. Many of the 
stimuli recorded by Duggar ( 12 ) in his spore germination studies—e. g., 
alcohol and organic acids—are known to be depressants of the surface 
tension of water. He states, however, that “attempts to increase the 
surface tension by means of small quantities of oil in the water gave 
only negative results.” 
Melhus and Durrell (54, p. 132-134) recorded stimulation of germina¬ 
tion of urediniospores of Puccinia coronata Cda. by the use of vaseline 
and paraffin oil. They state that “just how this oil brings about this 
stimulation is not known, but it is apparent that the surface tension of 
the water is changed.” 
Studies by the writer indicated that changes in the surface tension 
of the medium appeared to have but little effect on the germination of 
spores of Urocystis tritici. Aqueous solutions of sodium ricinoleate and 
sodium oleate were used. The surface tensions ranged from 72 dynes to 
38 dynes, but no significant results were obtained. It was found, how¬ 
ever, that very dilute solutions of a number of soaps resulted in germina¬ 
tion of the spores (Table IV). Observations were not made on the 
surface tension of these solutions which were more effective than dis¬ 
tilled water but less effective than many of the stimulatory substances 
discussed above. 
Sodium stearate solution, 1 part to 4,000,000, had the most marked 
effect. It is evident that in such a concentration there is only a very 
slight change in the surface tension of the fluid as measured against air. 
It is not known whether the soap or the hydrolytic products were 
effective in these cases. The spores failed to germinate in very dilute 
solutions of potassium hydrate, and hence the soap itself or the fatty- 
acid radicle appears to have been responsible for the change. 
Observations were made on the surface tension of the solutions of 
benzaldehyde and of butyric acid when in concentrations suitable for 
the germination of the presoaked spores of Urocystis tritici . 
