Feb. i6, 1924 
Flag Smut of Wheat 457 
ACTION OF PLANT ROOTS 
It is noted by the writer (35) that the addition of uninjured wheat 
seedlings to dishes of distilled water containing presoaked spores stimu¬ 
lated germination almost to the same extent as did the addition of small 
portions of plant tissue. 
Several investigators have reported that the presence of the host may 
profoundly affect germination of spores of parasitic organisms. 
Brown (5) has observed that drops of distilled water placed on the 
surface of leaves and floral structures of a number of plants stimulated 
the germination of spores of Botrytis cinerea Pers. This stimulation was 
correlated with an exosmosis of electrolytes from the host tissue, as 
indicated by increased electrical conductivity of the drop. 
Chupp (8) states “that the spores of Plasmodiophora brassicae Wor. 
do not germinate at ordinary room temperatures (16 0 to 21 0 C.) but do 
so readily when placed in test tubes on agar with young cabbage seed¬ 
lings. The presence of the host seems in some manner to exert an 
influence which to a certain extent takes the place of that offered by a 
greater amount of heat.” 
Among some phanerogamic parasites, also, there is evidence that the 
presence of the host may be necessary in order to supply the stimulus 
for germination of the seed of the parasite. Duggar (12) has called 
attention to the work of Koch and Heinricher on germination 
of seeds of Orobanchaceae. Heinricher makes the interesting observa¬ 
tion that the seeds of the parasite germinate in “periods of greatest 
humidity ” when in the presence of the host plant. A substance excreted 
from the host plant evidently furnished the necessary stimulus, although 
its nature had not been determined. 
More recently McWhorter (52) records the work of Kusano on 
Aeginetia indica, an Orobanchace parasitic on sugar cane. Kusano 
observed that “ the seeds of the parasite lie in the soil for months waiting 
for the rootlets of some holophytic plant to come near enough to furnish 
the stimulus necessary for their germination. They can not germinate 
until the actual contact with a suitable host is attained. The roots of 
the wrong host will make the seeds start germinating, but they can not 
complete germination until the roots of a suitable host find them.” 
In further tests with spores of Urocystis tritici it has been found that un¬ 
injured seedlings of other plants, namely, field peas and beans, stimulated 
the germination of spores which had been prespaked in distilled water, 
although the percentage of germination was not so great as in the in¬ 
stances where wheat or rye seedlings were used (Table I). These 
spores did not germinate as rapidly as those of the cultures in which cut 
tissues were used. It is an interesting fact, however, that so many 
spores germinated, and particularly that nonsusceptible plants should 
have such a marked influence in this respect. The results are given in 
Table I. The spores were sown on April 4, incubated at 22 0 C., and the 
different seedlings added on April 10. 
