426 
AMERICAN JOURNAL OF BOTANY 
[Vol. 9, 
As cultures grew in the greenhouse, they would be attacked during the 
later stages by Erysiphe graminis; the high-nitrate cultures were particularly 
susceptible to this fungus and could be readily picked out from the others 
by this fact. Medium-nitrate cultures were not so badly affected, and the 
low-nitrate cultures scarcely at all. This susceptibility to the fungus, vary- 
ing with the nitrate concentration in the nutrient solution, was constant 
for the three sets of experiments conducted with barley and was independent 
of the total concentration. There seems to be a direct relation between the 
nitrate concentration and the plant's susceptibility to the fungus in question. 
Experiments are being conducted to throw some light on the mechanism 
of this relationship. 
Table 4. Experiment I {Barley); Ratio of Tops to Roots as Nitrate Concentration is Increased 
{Dry Weights in Grams) 
Tops 
Sol. I (Low Nitrate) 
SoL II (Medium Nitrate) 
SoL III (High Nitrate) 
Roots 
Tops 
Roots 
Tops 
Roots 
Tops 
Roots 
Tops 
Roots 
Tops 
Roots 
Series i, 
14 days 
•2145 
.1606 
.1830 
.1620 
.0644 
.0510 
•0517 
.0525 
3-33 
3-15 
3-54 
3-09 
.2180 
.2000 
.i960 
•2135 
.0690 
.0627 
.0524 
.0670 
3-159 
3.189 
3740 
3.186 
.2462 
.2320 
.2179 
.2234 
•0635 
.0512 
•0583 
.0510 
3.88 
4-53 
374 
4-38 
Total . . 
.7201 
.2196 
•8275 
.2511 
•9195 
.2240 
Mean . . 
3.28±.o68 
3.32^.095 
4.i3±.i29 
Difference High Nitrate — Medium Nitrate = .81 dz .160. 
Series 2, 
21 days 
.3079 
•3525 
.4691 
.3882 
.0722 
.0845 
.1074 
•0953 
4.26 
4.17 
4-37 
4.07 
.4266 
.4287 
.4487 
•4045 
.1008 
.1050 
.1030 
.0861 
4-23 
4.08 
4-36 
4.70 
.4500 
.5591 
.5000 
•3625 
.0813 
.1105 
.0979 
.0709 
5-53 
5-06 
5-II 
5-II 
Total . . 
1-5177 
•3594 
1.7085 
-3949 
1. 8716 
.3606 
Mean . . 
4.22 ±.0431 
4.34±-o88 
5.2o±.o74 
Difference 
High Nitrate 
— Medium 
Nitrate 
= .86 ± .115. 
Series 3, 
28 days 
.8500 
•7645 
.6814 
-8697 
.1889 
.1700 
-1552 
.2121 
4-50 
4-49 
4-39 
4.10 
.9100 
•8155 
.8965 
•9175 
•1675 
•1573 
.1770 
.1878 
5.43 
5.12 
5-07 
4.89 
.9500 
.9200 
.8880 
.8251 
.1700 
•1477 
.1500 
•1559 
5-59 
6.23 
5-92 
5-29 
Total . . 
3-1656 
.7262 
3-5395 
.6896 
1 3-5831 
.6236 
Mean . . 
1 
4.37±.o63 
5.i3±.076 
5-75±-i36 
Difference 
High Nitrate — Low Nitrate = 1.38 zb .149. 
