Oct. 1, 1925 
Resistance of Maize to Sodium Chloride 
637 
RESISTANCE OP SEEDLINGS WITH VARIOUS STAGES OF 
PLUMULE DEVELOPMENT 
After finding that the older seedlings could be more easily and 
accurately classified by the stage of plumule development than by 
the length of radicles, the seedlings, in all of the later experiments 
after being sorted and placed on the disks, were allowed to remain 
in tap water until the youngest group reached the stage when the 
leaf roll had just emerged from the tip of the coleoptyle, then the 
disks, each containing 100 plants, were floated on the salt solutions. 
The percentage of seedlings of different sizes which survived an ex¬ 
posure of 96 hours to the salt solution (22,000 parts per million) is 
shown in Table III. 
X 
Table III. — Comparison of the percentage of seedlings at different stages of plumule 
development surviving after 96 hours in salt solution {22,000 parts per million) 
Date 
Well out of 
coleoptyle 1 
Just prior to 
unfurling 
first leaf 
First leaf 
unfurled 
Second leaf 
appearing 
1924 
May31_ _ __ 
15.2i2. 67 
19.0±2.65 
7. Oil. 72 
7.2il. 72 
20.0i2. 69 
53. 5i3.11 
7.0i2.35 
Do _ 
Do _: _ ' 
June 3 _ __ ; 
61.0i3. 29 
44.0i3.35 
17. 3i2. 53 
' 26.0±2,96 
21.0i2. 75 
25. 3i2.92 
- 
Do _ _ 
June 9 _ _ __ _ n _ w 
10.0i2.02 
10.0i2.02 
. 9.4il.99 
3. Oil. 25 
June 15_. . _ ...... * 
Do.....:._ . .... 
June 25_ ._ _ .. 
10. 9i2.11 
20.0±2. 69 
35. 0i3.22 
6.4il. 63 
Do _ _ _ 
Do _,_ 
X 
July 1 __: 
42.2i3.23 
32. 5i3. 32 
32'. 0i3.14 
25. 0i2.92 
31.0±3.12 
54. 5i3. 07 
15. 3i2. 59 
12.3i2.44 
Do _ _.... . ... 
July 6 _i__ . . _ . .. 
8. Oil. 83 
Do _IV.-l...__ _. _ 
July22 ______ ... 
16. 7i2. 53 
5. 5dbl. 82 
9.4i2. 01 
Do _ _ . 
^ .. .? -X-’a * 
1 The radicles at this stage were from 60 to 100 millimeters long. The other three groups represent a 
more advanced stage of growth than classification shown in Table II. 
From the data in Table III it is apparent that there is a critical 
stage in the development of the seedlings at which their metabolic 
functions are less interrupted by toxic salts than at any other time. 
This stage occurs about the time when the first leaf has pushed out 
of the coleoptyle for 10 or 15 millimeters, and but a few hours before 
it begins to unfold into blade form. An explanation for this might 
be found by determining the rate of reduction of the stored food in 
the endosperm, and the stage at which the seedling begins to decline 
in. vigor when not provided with nutrient material from an outside 
source. 
While the data shown in Table III are far from consistent, es¬ 
pecially when comparing results obtained from series of plants 
handled on different dates, they seem, however, to indicate clearly 
that the stage of development is of primary importance in determin¬ 
ing the relative resistance of seedling to toxic salt solutions, and that 
the most resistant stage to sodium chloride is just prior to the un¬ 
folding of the first leaf (fig. 1, stage No. 2).- When the data are 
studied under one date at a time, it will be observed that there are 
no discrepancies; all the results indicate an increasing resistance as 
seedlings develop after first sprouting, until the leaves begin to 
unfold, and then a diminishing resistance as they become older. 
71486—26f-4 
