*34 
Journal of Agricultural Research 
Vol. XXVII. No. 3 
Table 111.—Showing the P E value of the cell sap of the different organs in late-flowerinq 
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Date of observation and part of plant used. 
July 12 : 
Apex. 
Top leaves. . . 
Tower leaves.. 
July 15 (and 17 ):& 
Apex. 
Top of stem. . . 
Middle of stem 
Base of stem. . 
Roots (fibrous). 
July 20 : 
Top leaves 
Tower leaves... 
July 21 : 
Apex. 
Top of stem. . . 
m j j Plants exposed to natural 
Plants exposed to natural J length of day from date of 
loti/r+h _- J. j r • . • _ 
length of day from date of 
germination 
Hour of sampling. 
9- J 5 a . 
*•35 P- 
.... do 
m. 
m. 
m. 
9.05 a, 
.... do 
11.15 a 
... .do... 
1.50 p. m 
m.. 
2 p. m. 
.. .do. 
11.20 a. m, 
-do_ 
Ph value. 
5- 23 
5 . 22 
5- 59 
5 .18 
5- 30 
5- 43 
5- 46 
5- 46 
4. 98 
5- 65 
4. 98 
5- 14 
germination to June 28 and 
thereafter exposed to a 10- 
hour day. 
Hour of sampling. 
9.15 a. m.. 
11.30 a. m 
-do_ 
9.15 a. m 
.do... 
11.25 a 
.... do 
2 p. m. 
m. 
11.30 a. m. 
-do.... 
9.15 a. m. 
-do... 
a Flower buds only. 
b Observations of plants under the 10-hour day conditions were made on July 17. 
Ph value. 
a 5- 5* 
5-48 
5.81 
0 5- 84 
5- 47 
5- 47 
5-43 
5-46 
5 - !5 
5- 79 
“ 5-63 
S- 49 
To obtain further information on the relative acidity of the different 
organs of the plant as affected by the length of day, observations were made 
on plantings of cosmos which germinated May 24. One series was 
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P 10 - 5 -—Showing the effect of abrupt change in light exposure from the long days of summer to a io-hour 
day, on the active acidity of the sap in the apex of late-flowering cosmos (Table I). There is a prompt 
drop m active acidity to a level which is far below that characteristic of the advanced vegetative stage 
and the same as that exhibited in plants exposed to a io-hour day from the outset. Here, again (com¬ 
pare fig. 4), the active acidity of the open blossom is practically identical with that of the apical bud in 
the advanced vegetative stage which results from a long-day exposure. 
exposed to the natural length of day throughout the test and a second 
series was transferred from the full day length to a io-hour day on June 
28. Flower buds were found on the latter series on July 8. The data 
obtained are given in Table III. For the sample of top leaves the three 
