the Broad Bean and certain other Plants. 
643 
or so, little if any difference was evident between the plants treated with the 
two concentrations of boric acid, viz. 1 : 50,000 and 1 : 2,500,000 ; but a con¬ 
trast became apparent later, being especially marked in the sets grown for 
twenty days in the two solutions (Table III). Three weeks after the removal 
of IT3BO3 all the plants previously treated with the smaller quantity were 
‘dying off’, while those grown in the stronger solution were perfectly 
healthy and still in flower. In general ‘ dying off’ set in about three to five 
weeks after the removal of boron where 1 : 2,500,000 H 3 B 0 3 had been 
supplied, while withering was not apparent until four and a half to six weeks 
after the plants were transferred from a solution containing 1 : 50,000 H 3 B 0 3 , 
so that, on the whole, the larger quantity of boron was of more value to the 
plant than the smaller application, when the treatment lasted for a limited 
period only. 
The upward sequence of the dry weights (Table III and Text-fig. 3, B) as 
the treatment with boric acid was prolonged corroborates what has already 
been described. It is evident that but little dry matter is laid down after 
‘ dying off’ occurs, for of the plants which were carried on for the additional 
twenty-six days, only those which did not show signs of withering at the 
beginning of this period, i. e. those supplied with H 3 B 0 3 for at least forty days, 
were able to continue growth. 
Table III. 
Mean Dry Weights of Broad Bean Plants deprived of Boric Acid at 
Different Stages of Growth. 
Average of 5 plants. 
Aug. 9- 
■Oct. 18, 
1922. 
Aug. 
9-Nov. 
13 ? 1922. 
1 : 50,000 H 3 B 0 3 . 
1:2, 
500,000 
H z BO y 
Days in 
II z BO z . 
Days without 
// 3 Z> 0 3 . 
Root. 
Shoot. 
Total. 
Days without 
JJ 3 B 0 3 . 
Root. 
Shoot. 
Total. 
grm. 
grm. 
grm. 
grm. 
grm. 
grm. 
0 
70 
0.95 
6-21 
7-16 
96 
o-8i 
5.86 
6-67 
10 
60 
1.26 
6-o8 
7*34 
86 
1.00 
6-53 
7-53 
20 
5 ° 
1.88 
9.46 
n -34 
76 
i -53 
7.20 
8-73 
30 
4 ° 
2.26 
11.22 
13.48 
66 
1.66 
9.46 
11 • 12 
40 
30 
2 *53 
n-6o 
I 4* 1 3 
56 
2-55 
13.89 
16-44 
5 ° 
20 
2.49 
11.46 
13-95 
46 
2.90 
14.70 
17-60 
60 
10 
2.38 
10-71 
13.09 
36 
3 - 7 i 
15-74 
19-45 
7 o 
0 
3*°4 
11.23 
14.27 
0 
3 ,]C 5 
16.08 
19.23 
From the foregoing experiments it is clear that a small quantity 1 of 
boron supplied some factor essential to the growth of the broad bean plant 
that was lacking in the usual nutrient solution. 
Maze ( 23 ), in a somewhat similar manner, has claimed that among 
other elements boron is essential to the development of Zea Mays. 
1 The total quantity of boric acid supplied varied with the duration of the experiment from 1-20 
to 2*64 mg. H3BO3 where the concentration was I : 2,500,000. On an average each plant would have 
access to 0.2 mg. boric acid per week, but it has not yet been ascertained whether the whole of the 
quantity is taken up. 
