454 
Journal of Agricultural Research 
Vol. XXVII, No. 7 
which, may occur during germination. Each spore may produce a pro¬ 
mycelium, usually about 30/* in length, which characteristically produces 
several prolongations which are usually considered sporidia. The spo- 
ridia are usually 30 by 5/1 in size. A variable number may be produced 
on the promycelium, although from two to four occur most frequently. 
These structures may be formed under the surface of the medium in 
which the spores are germinating, at the surface of the medium, or in the 
air when only a portion of the spore is in contact with the substrate. 
Wolff (57) mentions that the germ tubes produced by the sporidia of 
Urocystis occulta may become detached and then may be widely dis¬ 
tributed by air. The writer has not observed that the sporidia or the 
sporidial germ tubes of U. tritici ever become detached. The sporidia 
characteristically germinate while attached to the promycelium. A germ 
tube is produced from the tip of the sporidium. It is fairly constantly 3 
microns in width and under favorable conditions it may grow to a con¬ 
siderable length (from 3 to 4 mm. in solid nutrient media). The sporidia 
were observed to fuse occasionally, although this did not appear to be a 
characteristic feature at germination. 
PHYSIOLOGICAL STUDIES 
INTRODUCTION 
There is little need to stress the importance of a knowledge of the con¬ 
ditions which govern germination of the spores of parasitic fungi. Other 
conditions being favorable, the severity of an outbreak of a disease fre¬ 
quently is determined in the first instance by the number of spores which 
cause infection of the host. As it has been shown that epidemics of flag 
smut frequently are traceable to the presence of viable spores in the soil, 
and as, under those conditions, control by present known methods of seed 
treatment is not possible, it appears especially desirable that we should 
have a more complete knowledge of the reaction of the pathogene to its 
environment, for the factors favoring germination and subsequent growth 
of the fungus must necessarily be closely related to those primarily re¬ 
sponsible for the development of the disease. 
The spores of Urocystis tritici have long been known to germinate 
capriciously. The writer (35) has referred to the difficulties experienced 
in obtaining results from spore germination studies and has described a 
method of stimulating spore germination. Spores which had been pre¬ 
soaked in water for several days germinated readily after the addition of 
small quantities of certain plant tissues. Tissues from wheat and rye 
plants were found to be the most effective. 
Although not a characteristic feature of the spores of all smut fungi, 
those of many species do not germinate readily. Potter (38) speaks of 
the difficulty experienced in attempting to germinate spores of Sorosporium 
reilianum (Kuehn.) McAlp. In repeated tests in different seasons aqd 
at various times of the year, he noted only slight and irregular germina¬ 
tion, and states that rarely did more than 15 per cent of the spores 
germinate. 
Walker and Jones (52), in a study on Urocystis cepulae Frost, state that 
“the germination of the fungus spores has been so scanty that the effect 
of temperature upon the fungus has been necessarily limited to inocula¬ 
tion experiments with infected soil.” 
