Transpiration as a Factor in Crop Production. 157 
found by Fitting (1911) in the foliar cell sap of desert plants 
(something over one hundred atmospheres of osmotic pressure), 
possesses a vapor tension less than 10 per cent below that of pure 
water and should therefore evaporate more than 90 per cent 
as rapidly." 
EFFECT OF PROLONGED CONFINEMENT IN CANS OF SOILS 
DIFFERING IN FERTILITY. 
The plan of the experiment recorded in Table 66 has been 
discussed on page 143. Attention has been called to the fact that 
after the first year the plants lacked their normal thrift in these 
soils. They assumed a yellowish color and made poor growth as 
tho the soil had greatly deteriorated in available fertility. This 
effect is attributed to a lack of aeration under the conditions 
prevailing. The low productivity cannot in all probability be 
assigned to a toxic effect from continuous cropping to corn, for 
the reason that four years of continuous corn cropping under 
field conditions on similar soil does not appear to be similarly 
injurious. 
Table 66. — Summary showing plant growth and water require- 
ments of corn in six degrees of soil fertility during four con- 
secutive years, 1911 to 191 The potometers were filled in 
1911 and the same soil remained in them undisturbed thruout 
the period. 1 
Year 
No. of 
potom- 
eters 
averaged 
Dry matter 
Total water 
transpired 
Transpiration per 
gram 
Ear 
Total 
Dry weight 
of ear 
Total dry 
matter 
(1) 
(2) 
Grams 
(3) 
Grams 
(4) 
Kilograms 
(5) 
Grams 
(6) 
Grams 
(7) 
INFERTILE SOIL 
1911... 
4 
36.74 
112.75 
61.961 
1,686.47 
549.50 
1912... 
4 
12.83 
55.36 
29.215 
2,277.08 
527.73 
1913 
4 
9.67 
87.33 
62.362 
6,449.02 
714.10 
1914... 
4 
16.00 
76.25 
37.150 
2,321.88 
487.21 
Average 
16 
18.81 
82.92 
47.67 
3,183.61 
569.64 
INFERTILE SOIL 
WITH MANURE 
1911. . . 
4 
193.99 
375.82 
131.653 
678.66 
350.30 
1912. . . 
4 
114.63 
188.21 
47.432 
413.78 
252.02 
1913. . . 
4 
81.50 
215.25 
109.815 
1,347.42 
510.17 
1914 . . . 
4 
53.50 
163.25 
61.890 
1,156.82 
379.11 
Average 
16 
110.91 
235.63 
87.698 
899.17 
372.90 
1 S>ee footnote, p. 158. 
