66 
WATER REQUIREMENT OF PLANTS. 
Table LVI. — Effect of insufficient carbon dioxid in the air on the water requirement of 
rape, according to Sorauer (1880, p. 467). 
Duration. 
In free air. 
i 
Under bell jar. 
Under bell jar, with po- 
tassium hydrate. 
Number of 
determina- 
tions. 
Water re- 
quirement. 
Number of 
determina- 
tions. 
Water re- 
quirement. 
Number of 
determina- 
tions. 
Water re- 
quirement. 
Days. 
20 
4 
282 ±11 
3 
243±5 
2 
355 ±5 
CONCLUSIONS. 
The effect of the carbon-dioxid content of the atmosphere upon the 
water requirement appears to have been investigated only by Sorauer. 
He found the water requirement to increase when the carbon-dioxid 
content was diminished. This is in accord with what is now known 
regarding the role of carbon dioxid in photosynthesis. 
EFFECT OF PARASITES ON THE WATER REQUIREMENT. 
wimmer's experiments. 
Wimmer (1908) reported a series of experiments to show the effect 
of nematode-infested soil on the water requirement of sugar beets 
and celery. The results (Table LVII) show without exception an 
increase in the water requirement due to the action of the parasitic 
worms. This is probably due to the fact that infested plants grow 
much more slowly than those not infested, as is indicated by the 
weight of dry matter produced in each case. 
Table LVII. — Effect of nematodes 1 on the water requirement of sugar beets and celery, 
according to Wimmer. 
Crop and plat. 
Weight 
of soil 
per pot. 
Sugar beets: 
A7n 
Grams. 
f 8, 106 
\ 8, 106 
A8n 
[ 8, 106 
8,202 
Celery: 
A7n 
8,106 
A8n 
8,202 
Nema- 
todes. 
Fertilizer per pot. 
K 2 
P2O5 
Soil- 
moisture 
content. 
Mean of 
dry 
matter. 
Water 
require- 
/Dead. 
\Alive. 
(Dead. 
\ Alive. 
(Dead. 
\ A live. 
/Dead. 
1 A live. 
Dead.... 
Alive 
'Dead.... 
.Alive — 
Grams 
0.705 
.705 
.705 
.705 
.705 
.705 
Grams. 
0.224 
.224 
1.820 
1.820 
.700 
.700 
.224 
.224 
Grams. 
0.355 
.355 
.355 
.355 
.355 
.355 
.355 
.355 
.335 
.335 
.335 
.335 
Per cent. 
16 
16 
16 
16 
12 
12 
16 
14 to 15 
14 to 15 
14 to 18 
14 to 18 
Grams. 
47.8 
19.1 
75.9 
36.8 
45.4 
34.4 
21.9 
6.6 
52.2 
33.5 
40.5 
23.7 
419±4 
933 ±118 
336 ±11 
567 ±85 
395 ±14 
474 ±26 
710±41 
,083±57 
269 ±49 
368±152 
422±20 3 
521 ±4 
1 The nematodes were killed by carbon-bisulphid treatment. Computed from Wimmer's data (1908. pp. 
142-143, 154-155). A7n is the mean of two determinations, A8n the mean of three, except as noted.' 
2 Mean of four determinations. 
3 Mean of two determinations. 
285 
