on Plant Growth in Nutrient Solutions, &c. 365 
» 
solutions, and in the modified Tottingham solutions as described in Table I, 
when supplied with suitable forms of inorganic iron in concentrations which 
were found in the preceding experiments to be approximately optimal for 
the growth of these plants. Three series of cultures were conducted simul¬ 
taneously. The nutrient media used with two of these series, which will be 
designated series E and series F, consisted of the Tottingham solutions 
(Table I) supplied with iron in the form of ferric phosphate and ferrous sul¬ 
phate, respectively, corresponding solutions of the two series being alike in 
every respect except in the form and amounts of iron used. The third 
series, which will be designated the ammonium-sulphate series G, was carried 
out with the modified Tottingham solutions previously described (Table I) 
Ferric phosphate in quantities of 2 mg. per litre of nutrient solution wa$ 
added to each solution of series E and series G whenever these were pre 
pared. At the time of each solution renewal, freshly prepared ferrous 
sulphate in solution form was added to each of the nutrient solutions 
of series F in very small quantities, sufficiently large, however, to prevent 
chlorosis in the plants, but not enough to produce serious specking of 
the leaves in any culture. In the course of the nine solution renewals which 
were made during the growth period, each culture of series F received 
a total of approximately 2-5 mg. of iron in the form of ferrous sulphate, 
while each culture of series E and F received during the same time 18 mg. 
of iron in the form of ferric phosphate. The record indicating the nature of 
the environmental conditions to which the cultures were exposed during the 
growth period is given in Table III. 
Table III. 
Maximum and minimum temperatures , average daily zvater loss by evapora- 
tion from standard white and black spherical atmometers , and character 
of days for the experimental period. 
Experimental period 
1921. 
Air tem¬ 
perature. 
Average daily 
evaporation} 
Radio- 
evaporation . 2 
Number of days. 
,-^ 
' N 
,-*- 
_ y 
-JC 
—- 
A 
r U 
Beginning. 
Ending. 
S 
s 
ci 
• 
s 
P 
g 
• 1-^ 
15 
Maximum. 
Minimum. 
Average. 
Maximum. 
Minimum. 
Average. 
Clear. 
0 
0 
r—> 
t- 
ci 
c- 
Cloudy. 
°C. 
°C. 
c.c. 
c.c. 
c.c. 
c.c. 
c.c. 
c.c. 
July 24 
Aug. 29 
42.0 
13*5 
26-1 
2-2 
16.0 
6.1 
0.2 
3'6 
22 
9 
5 
In general, all the cultures appeared quite healthy on the harvest date. 
1 Evaporation was measured by means of the Livingston standard spherical atmometers. 
Livingston, B. E.: Atmometry and the Porous Cup Atmometer. Plant World, 18, 21-30, 51-74, 
95-m, 143-49, I 2 9 I 5 - Reprinted, Tucson, 1915. 
2 The values given for radio-evaporation represent the average daily excess ot water loss from 
the standard black spherical atmometer over that from the white. 
B b 
