460 
Journal of Agricultural Research 
Vol. XXVII, No. 7 
Since it had been shown that the materials which stimulated germina¬ 
tion of the spores of Urocystis tritici were volatile in steam, tests were 
made to determine if these materials would volatilize at lower tempera¬ 
tures. 
Presoaked spores of Urocystis tritici were placed on the surface of a few 
cubic centimeters of distilled water in Syracuse dishes. The dishes were 
then placed in a vessel which contained a small quantity of expressed sap 
of wheat seedlings, and the container was then sealed. After 18 hours at 
22 0 C., over 50 per cent of the spores had germinated in each of the three 
trials. There was no gemination in the controls. It is possible in these 
cases that the stimulus may have been derived from some of the original 
constituents of the plant sap, or it may have been derived from some of 
the products of its decomposition, possibly organic acids, esters, or 
alcohols. 
The spores of Urocystis tritici did not germinate readily in solid media, 
although many different nutrient substrata were used. However, pre¬ 
soaked spores germinated in wheat plant extract agar or in agar contain¬ 
ing appropriate concentrations of the distillate from such extracts. At¬ 
tempts were made to sterilize the surface of the spores by washing them 
in one-half per cent solution of copper sulphate for periods up to two 
minutes before transferring them to sterile distilled water for presoaking 
and subsequent transference to the solid media. 
Under these conditions it was not found possible to eliminate entirely 
all bacterial contamination. However, the spores produced normal 
sporidia, which in turn produced germ tubes which grew to a length of 4 
mm. after four weeks at 7 0 C. The manner of growth was similar to that 
previously recorded in liquid media. The protoplasmic contents re¬ 
mained segregated at the tip, while the remainder of the germ tube 
became septate and apparently was devoid of contents. There appeared 
to be no increase in the amount of protoplasm in the germ tube. 
It is not known whether such germ tubes are capable of producing 
infection. There is the interesting possibility, however, that the infec¬ 
tion capabilities of the organism may be increased by such an extended 
growth period under soil conditions. 
NATURE OF STIMULUS 
The identification of the activating constituents of the distillates of 
wheat-plant decoction is very difficult. The stimulus appeared to be 
most efficient when the distillates w r ere highly diluted. The distillates 
obviously are complex in composition and the individual components 
might be expected to function very differently on spores exposed to their 
action. Several attempts were made to determine if the activating sub¬ 
stances belonged to any general group of chemical substances. “ Func¬ 
tional” distillates were used, i. e., distillates in which presoaked spores 
germinated readily. These were acidified with sulphuric acid and redis¬ 
tilled. The original distillates also were made alkaline with barium 
hydroxid and then redistilled. Subsequent germination tests with these 
products of the second distillation showed that in each case they were 
as potent as the original distillate. 
It would thus appear either that a number of the original constituents 
of the wheat plant decoction were operative or that the stimulus came from 
some ingredient which was unaffected in either acid or alkaline solution. 
