Nov. 1,1925 
Ophiobolus yraminis and TaTce-All of Wheat 
813 
though the difference in the rate of growth of these two sets of cul¬ 
tures was only slight, it was generally constant. The variation in 
temperature between the two groups of cultures was never more 
than 1 degree, and as the studies on the influence of temperature on 
the rate of growth of the fungus show that differences of 1 degree or 
less make little difference in the rate of growth, it is concluded that 
the decrease in growth of the cultures placed in the light was due to 
the influence of light and not to that of temperature. 
Table IV .—Influence of light on the growth of mycelium of Ophiobolus graminis 
[Data based on 7-day-old cultures] 
Strain of fungus 
Agar medium used 
In light 
or dark 
Diameter of colonies in centimeters 
New York.. 
Potato-dextrose_ 
Light. 
8.0 
8.0 
8.0 
8.0 
8.0 
8.0 
8.0 
.do__. 
Dark. 
8.5 
8.5 
8.5 
8.5 
8.5 
8.5 
8.5 
String bean.. 
Light_ 
7.0 
8.5 
7.0 
7.0 
7.0 
7.0 
7.0 
.do.. 
Dark.. 
7.0 
7.5 
7.5 
7.5 
7.5 
7.5 
7.5 
Oregon__ 
_do___ 
Light_ 
4.0 
4.5 
4.0 
4.0 
4.0 
4.5 
4.0 
.do.. 
Dark. 
4.0 
5.0 
4.0 
4.0 
4.5 
4.5 
5 0 
.do. 
Light_ 
2.5 
2.5 
3.5 
3.0 
2.5 
2.5 
3.0 
_do...__ 
Dark.. 
3.0 
4.0 
3.5 
3.0 
3.0 
3.5 
4.0 
The influence of light on sporulation was very marked in contrast 
to its influence on the growth of mycelium. With string-bean agar 
as a substratum, no culture kept in absolute darkness formed even 
a single perithecium, while most of those kept in the light formed 
fruiting bodies abundantly, as shown in Table V. One hundred and 
ninety-six cultures were observed at three different times and in all 
cases only mycelium was produced in those incubated in the dark. 
However, a few of the cultures kept in the light did not sporulate, 
which indicates that some influencing factor favorable for sporula¬ 
tion remains yet to be determined. The writer does not infer that 
perithecia will form only in the presence of light, for they occasionally 
are found on the roots of plants near the crown where they are 
formed in darkness, but from the laboratory experiments cited it is 
a arent that light favors the development of perithecia on the 
ure media used and under the conditions described. 
Table V .—Influence of light on the development of perithecia of Ophiobolus graminis 
[Data based on 47-day-old cultures] 
Experiment No. 
1 
3 
In light or 
dark 
Total 
number 
of cul¬ 
tures 
Number 
of cul¬ 
tures 
produc¬ 
ing peri¬ 
thecia 
/Light... 
20 
14 
[Dark. 
20 
0 
/Light- 
60 
46 
\Dark—. 
40 
0 
/Light- 
36 
30 
[Dark_ 
20 
0 
PATHOGENICITY OF THE FUNGUS 
All three strains of the fungus used in these studies were patho¬ 
genic on wheat plants. To prove this, disinfected Goldcoin wheat 
was sown in soil that had been disinfected by steam and subsequently 
74333—26f-2 
