458 
Journal of Agricultural Research 
Vol. XXVII, No. 7 
Table I .—Effect 
of uninjured plant tissue on the germination of spores of Urocyslis 
tritici presoaked in distilled water 
Num¬ 
ber of 
dish. 
Plant. 
! Percentage of germination on— 
Apr. 10. 
| Apr. 11. 
Apr. 12. 
Apr. 13. 
96 
Wheat. 
! O 
i 
; 08 
* 
97 
.do. 
0 
OO 
98 
.do. 
0 ; 
8c 
99 
Rye. 
O : 
! 87 
100 
.do. 
! 
O 
1 01 
1 
.do. : 
0 i 
72 
2 
Field pea. 
0 
Trace. 
Trace. 
3 
.do. 
0 
21 
4 
.do. 
0 
2 
5 
Bean.I 
0 
c 
6 
.do. | 
0 
0 
7 
.do. 
0 
xx 
8 
Control of distilled water.j 
0 
0 
0 
0 
9 
.do. ! 
0 
0 
0 
0 
It is possible that such a relationship may have a very fundamental 
bearing on the question of the epidemiology of the flag-smut disease. 
The soil solution is of complex and varying composition. Laboratory 
studies on the germination of spores in soil extract solutions also have 
shown that the spores will germinate more profusely on the addition of 
young tissues of various plants. Hence, although it is not possible to 
duplicate soil conditions in the laboratory, it would appear that at certain 
times certain facts observed under controlled conditions in the laboratory 
may at least be duplicated in the field. When there is adequate moisture 
in the field, the presence of actively growing plant roots alone may be 
expected to stimulate the germination of many spores of Urocystis tritici 
and thus reduce the amount of viable inoculum between successive crops 
of the susceptible host. It is a matter of common observation that, under 
normal conditions, when supplied with an adequate supply of oxygen, 
plant roots excrete carbon dioxid; when insufficiently supplied with 
oxygen, the products of anaerobic respiration are carbon dioxid, alcohol, 
and various organic acids, such as formic, acetic, and lactic. 
It is apparent that the most marked stimulation of the spores is to be 
expected when the environment causes a certain amount of anaerobic 
respiration of the host roots. It is not known whether the organic acids 
or the alcohols are primarily responsible for the germination observed, or 
whether certain other constituents of the plant are effective, for subse¬ 
quent studies have indicated that small amounts of other volatile sub¬ 
stances are effective in this respect also. 
EFFECT OF PI^ANT TISSUE EXTRACTS 
Reference has been made to the fact that young tissues of a number of 
plants stimulated germination of presoaked spores of Urocystis tritici. 
A number of investigators have observed that plant decoctions form a 
very suitable medium for the germination of spores of many organisms. 
Anderson ( i) has shown that the germination of pycnospores of Endothia 
parasitica Murr. is slight and uncertain when sown on tap water, rain 
