200 
WILBER BROTHERTON, JR., AND H. H. BARTLETT 
gradual increase in length from the base upward, to a maximum. After 
the maximum mean length is reached, there is a decrease toward the 
upper end of the internode, but not a decrease to the minimum which 
occurs at the base. The gradual increase in cell size may possibly be 
partially accounted for by increase in the amount of water available 
during the elongation of the internode. When the seedling is very 
young the root system is simple, and relatively inadequate. More- 
over, the differentiation of conductive tissue is not complete. Con- 
sequently the cells cease expanding earlier than do subsequently 
formed cells, which have the advantage of a copious water supply and 
a more highly developed conductive system. In attributing to water 
supply a possible influence upon the size of epidermal cells, we do not 
commit ourselves to any theory as to the cause of extension. Whether 
extension is due to turgor pressure or not, the process could not take 
place at all without sufficient water to keep the protoplasm in contact 
with the cell wall, and that amount would hardly be measurably 
different for a moderately rigid cell wall whether the turgor pressure 
were great or small. 
Table VII 
Length in Mm. of Undivided Primary Epidermal Cells of Epicotyl of Plant Grown in 
Dark 
Class 
1 
Section 
Entire 
Internode 
I 
2 
3 
4 
6 
7 
8 
9 
10 
.060-.II7 
1 
■■ 7 
I 
2 
4 
I 
4 
3 
6 
II 
40 
•I2O-.177 
. . 30 
3 
4 
10 
3 
9 
12 
6 
4 
19 
100 
.180-237 
■•1 4 
3 
I 
4 
6 
4 
2 
6 
30 
.240-297 
I 
3 
2 
6 
Table VIII 
Length in Mm. of Divided Primary Epidermal Cells of Epicotyl of Plant Grown in Dark 
Class 
Section 
Entire 
Internode 
2 
3 
4 
5 
6 
7 1 8 
9 
ID 
.060-. 117 
0 
3 
0 
0 
0 
0 
I 
I 
7 
.120-177 
12 
6 
12 
5 
. 5 
5 
5 
9 
4 
68 
.180-237 
30 
24 
22 
25 
40 
17 
4 
15 
14 
16 
218 
.240-297 
II 
30 
30 
30 
18 
27 
28 
25 
26 
12 
237 
•3OO-.357 
5 
16 
II 
18 
15 
17 
12 
18 
II 
146 
.360-417 
8 
7 
7 
13 
8 
12 
9 
78 
•42O-.477 
4 
2 
I 
5 
8 
4 
8 
6 
7 
45 
.480-.537 
I 
I 
2 
2 
2 
8 
2 
2 
21 
•54O-.597 
2 
2 
4 
