20 
Cul.oRADo ExpekimKiNT Station. 
liad been subjected. Later herein we shall g'ive the held evidence 
that there was in Colorado a fungus or infection factor in the leaf- 
roll disease. 
Figures 9, 10 and ii show the condition of the plants after 
80 days of growth. The sign (—) means that Fiisariiuu was 
absent and the sign (- 4 -) means that Fusarium was found. The 
first figures are the percentages of moisture used, the second the 
temperatures. Where another number is used below a line it 
represents the condition as changed for the last five days. 
The following table, Figure 12, shows dividing lines between 
plants injuned and not injured by Fusarium because of heat and 
soakage. 
JO fa 65° 
ZOf 65" 
ZOf 65" 
ZOf 65" 
30f 65°^ 
65° . 
i-Ofi 65°' 
_ 
/Of 
/Ofo 30^^^ 
30'' , 
zof 30" fy 
. 
30f 30° ~ 
zof. sa° J. 
4-0 60° ^ 
/O^ <50° 
/O^ 95° 
ZOf 50" 
ZOf 95° 
Izofo 50° , 
50 fo 95° ' 
/ 
I30f 30° , 
/ ^Of 95° 
/ 
/of e5'’ 
/0% 95° 
ZOfo 65" _J 
ZOf 95° J 
ZOf 65° J 
50f 95° Jj 
30% 65° , 
40f 95° 
/of 30'’ 
10% 95° , 
30" , 
^ ZOfo 35° ! 
/ 
r zo% &o° , 
50f 95° 
30% 60° 1 
40% 95° ~ 
/0% 50° 
~1W ^o° 
Hooded 1 
rv\//ce 
Hooded 
Onco 
ZOf 30"’ 
ZOf 30^ 
Figure 12.—Giving summary of greenhouse studies of potato health. Per¬ 
centages of water in soil and temperatures of soil for first seventy-five days 
shown above the line, and for the next five days shown below the line in the 
form of a fraction in each case. Presence of disease is shown by a plus (-}-) 
sign. Absence of disease is shown by a minus (-) sign. Note that the com¬ 
bination of adverse factors governing the appearance of Fusarium in the ducts 
is limited by the solid lines drawn through the table. As the water was 
applied to the surface, the distribution of the water w.as not quite uniform 
throughout the soil, and it is therefore believed that a line somewhere near 
the position of the dotted line would more accurately represent the boundary. 
It would be desirable to repeat this experiment in summer, in 
dry air and sunshine, out of doors. There would be likelihood of 
producing the leaf-roll disease in typical form in some of the 
conditions and entirely healthy plants in others. 
