IV. Correlations in Development . 267 
An additional series (V), at the same temperature but using another 
variety of pea (round yellow) is given in Table III and Fig. 4. The results of 
this series are of the same type. Root growth after the appearance of 
secondary roots maintains a constant and apparently limited rate, while the 
stem rate is rising to a maximum. When the rate of stem growth shows 
a marked decrease root growth practically ceases. 
Table III. 
Average Dry Weight of Peas (round yellow variety). 
Series V (15-0° 
± 1-0° C>). 
Series VI (14-8° 
± 1*2° C.). 
Day. 
Shoot. 
Root. 
Day. Shoot. 
Root. 
0 
2.7 mg. 
8-6 ±0.2 mg. 
0 
2.5 mg. 
12.2+0.2 mg. 
1 
9-i ±0-3 
1 
3-4 
13.2 ±0.4 
2 
4 -i 
9.7 ±0.4 
2 
4.0 
T 4 * 3±°-3 
4 
S*3 ±0-4 
14.3 ±0.4 
3 
4.2 
I 4-7 ±°-4 
7 
25.2 + 1.0 
20.5 + 0-7 
4 
7.2 + o-6 
16-1 ±o-6 
8 
32.5 ±0.9 
21.7 ± o-6 
7 
16-3 + 1.0 
20.0 ±o»6 
10 
50-0 +1.4 
26-2 + o-S 
> — 
9 
21-3 ± i-8 
20.1 + 0.5 
12 
64.3 ±1.7 
29.8 + 0.9 
10 
23.5 ± 1.2 
20-0 + 0-4 
15 
78-1 +2*1 
32-0 ±0-8 
12 
3 U 5 + 1-2 
26-o± 0.8 
17 
81-0+ 2-7 
31-9 + 0-8 
14 
36*6 ± 1-3 
25-8 ± o-8 
i 7 
56.O+I.45 
32.4 + 0.9 
21 
63.2 + I.6 
31.9+ 1-0 
he possibility existed that the 
limiting 
of the oxygen 
supply to the 
roots might be the reason for the limited growth rate. This seemed to be 
disproved by the high growth rate obtained in the roots of Series III at 
a much higher temperature (25 0 C.), though otherwise under precisely 
similar conditions. Secondly, no increase in the rate of root growth was 
obtained by replacing the nutrient solution more frequently or by aerating 
it. In the third place, when oxygen deficiency did appear it produced 
a distinct stoppage of growth. This may be illustrated by Series VI 
(Fig. 3), in which the solution was left unchanged, but aerated on the third, 
tenth, and fourteenth days. The dish holding the solution was in this case 
much smaller and deeper, the plants being crowded together. The lateral 
roots grew vigorously on the surface of the liquid, but, except after aeration, 
the main root and submerged laterals showed little or no growth. The 
effects of deficient oxygen supply were very marked, in this case, and it is of 
interest to notice that the stoppage of root growth produced was associated 
with a marked reduction in the rate of stem growth—a feature not observ¬ 
able in the preceding series of observations. The facts clearly suggest, 
therefore, that the limitation of root growth rate in the earlier series was 
not due to deficient oxygen supply. 
Further, since changing the nutrient solution more frequently produced 
no effect, and since there was no change in the results when the nutrient 
solution was reduced to one-fifth of the strength used in the series cited, it 
