Transpiration as a Factor in Crop Production. 
63 
116.3 per cent in the smallest and 12.2 per cent in the largest. 
Manure reduced the water transpired per gram of dry weight 
73.7 per cent for the ear and 21.7 per cent for the entire plant in 
the smallest potometers. For the largest potometers these data 
are somewhat inconsistent in that manure actually increased 
the water requirement for the ear and the entire plant 9.0 and 
4.6 per cent, respectively. Doubtless, apparent inconsistencies 
are often due to the averaging together of an insufficient number 
of plants to overcome individuality. The reader is referred to 
the tables and charts for other relationships. 
A preliminary test of three different sized potometers was 
made the preceding year, 1913. The results which follow in 
Table 8 substantiate in principle the more extensive 1914 data. 
Table 8. — Summary showing effect of size of potometer upon growth 
and water requirements of corn. 1913. (Hogue's Yellow Dent corn.) 
Size of 
Mois- 
No. of 
Dry matter 
Total 
potom- 
ture- 
potometers 
water 
eter 
free soil 
averaged 
Stalk 
Ear 
Leaves 
Total 
transpired 
Inches 
Pounds 
Grams 
Grams 
Grams 
Grams 
Kilograms 
(1) 
(2) 
(3) 
(4) 
(5) 
(6) 
(7) 
(8) 
12x24 
86 
4 
104 
28 
33 
165 
90.01 
16x36 
245 
80 
168 
194 
54 
416 
165.22 
30x36 
933 
4 
214 
311 
74 
599 
197.06 
Size of 
potom- 
eter 
Total 
leaf-area 
Water requirement per 
Leaf- 
area per 
gram 
dry wt. 
Ratio 
of wt. 
of ear 
to wt. 
of stalk 
Height 
of stalk 
gram dry 
wt. of ear 
gram dry 
wt. of 
plant 
sq. in. 
leaf- 
area 
(1) 
12x24 
16x36 
30x36 
Sq. in. 
(9) 
680 
1,070 
1,440 
Grams 
(10) 
3,215 
852 
634 
Grams 
(11) 
546 
397 
329 
Grams 
(12) 
132 
154 
137 
Sq. in. 
(13) 
4.1 
2.6 
2.4 
(14) 
.30 
1.15 
1.45 
Inches 
(15) 
71 
89 
83 
It is evident from the data that the limitation of the soil thru 
the size of the potometer may be a great source of error in pot 
experiments. It seriously affects not only the transpiration 
relationships but the entire development of the plant. A modified 
test of the effect of the size of the potometer is planned in which 
the amount of manure added will be varied according to the 
amount of soil contained by the potometers. The soil unit 
rather than the plant unit will be taken as the basis for comparison. 
