Broivn: Groivth of Elodea 5 
Table I. — Groivth of 178 plants of Elodea, April 1 to 5. 
Growth. 
Number 
of 
plants. 
Growth. 
N umber 
of 
plants. 
1 
j Growth. 
Number 
of 
plants. 
Growth. 
Number 
of 
plants. 
Growth. 
Number 
of 
plants. 
Mm. 
Mm. 
Mm. 
Mm. 
Mm. 
3 
1 
10 
15 
16 
9 
22 
1 i 
28 
1 
5 
1 
11 
16 
17 
7 
23 
2 
CO 
1 
6 
5 
12 
19 
18 
3 
24 
2 
38 i 
1 
7 
13 
13 ; 
18 
19 
3 1 
25 
2 
39 1 
1 : 
8 
12 
14 ! 
' 19 
20 
2 i 
26 
1 
9 
15 
15 
5 
21 
2 ■; 
27 
1 
j 1 
An examination of Table I shows that the growth in length 
varied from 3 to 39 mm. Fifty plants which had grown from 7 
to 10 mm were used in the experiments recorded in Table V, and 
80 which had grown from 11 to 16 mm in those recorded in 
Tables IX to XL In placing the plants in the experiments, those 
which had made the same amount of growth were distributed as 
nearly equally as possible in the various jars. Each jar should, 
therefore, contain plants showing different rates of growth ; but, 
under the same conditions, these rates should vary much less 
than if no selection had been made. A comparison of table 1 
with tables 5 and 7 to 11 shows that the extent of the individual 
variations was decreased greatly by the selection. The indi- 
vidual variations should, moreover, be approximately equal in all 
jars; and consequently not a serious source of error. 
EFFECT OF COo, FROM THE SOIL, ON GROWTH 
A comparison of the amount of CO, which water will absorb, 
under ordinary conditions, with that used in photosynthesis by 
submerged plants, such as Elodea, would seem to show that the 
latter process would be greatly retarded unless CO,, from some 
source other than the air, is added to the water. One hundred 
cc of water at 20° will dissolve ^ 90.14 cc of CO 2 if exposed in 
an atmosphere of the same. The amount dissolved will decrease 
in proportion as the percentage concentration of CO, in the 
atmosphere decreases, so that, under ordinary conditions, water 
at 20° will always absorb from the air a smaller percentage of 
CO, than is contained in it. Air contains,’’ on an average, about 
’Thorpe, T. E. Dictionary of Applied Chemistry (1898). 
