ss 
32 
the cobalt paper withdrew water from the leaf during the first two periods 
more rapidly than it transpired from the free surface but much less 
rapidly during the last period. The change from an acceleration to a 
retardation occurred in about half an hour; it often appears more quickly. 
The measurement of transpiration by weighing cut pinne and their con- 
tainer was deemed unavailable when this experiment showed that the rate 
fell during a’ few hours to 8 per cent of the initial. As determined by 
the cobalt test, the rate fell during the same experiment to less than 2 per 
cent. This exhausts the really distinct methods of making continuous 
direct determinations of the transpiration of a single subject. 
Neither of these usually reliable methods being alone available in 
working on the coconut, I next had recourse to combinations, attempting 
to check a continuous experiment with one method by applying frequent 
corrections obtained from observations by the other; thus at the same 
time having the advantage of accuracy in the weighing method, and that of 
working with uninjured pinne on the tree by the cobalt test. I first tried 
to reach these ends by determining at intervals of several days the loss of 
weight of pinne placed in bottles of water, and at the same time com- 
paring the rate at which cobalt paper was turned red by these cut pinne 
with that at which it was altered when it was applied to pinne in sifw on 
the tree. My most satisfactory experiments of this kind furnished 
material for the following table: 
The pinne A, B, and C were cut on the afternoon of January 17 and the cut 
ends killed by insertion in nearly boiling water. The leaf D was freshly cut at 
2.30 p. m. January 18, and its ends not killed. All weights are in grams. The 
loss was determined regularly at one-hour intervals during the day. The bottles 
were hung in the tree, putting the pinne as nearly as was possible in natural 
conditions. The bottles themselves were shaded to prevent heating. 
Fem ati me poo ; 
Date. | Hour. | A.- 4: 3B. C. | dD | Behavior of cobalt paper.* | 
| 
a ae eel oe 
Jan, 17| 5.30p.m. pons conefpnnnncnefonn— oe = 
6.30. m, |-------- | 0,12 |--------|-------- 
7.30 a.m. 0.08 | = .02 0,02 Sceecameus Red in 8 minutes; leaves were damp. 
| 
| 8.380a.m. 14 | .09 .09 |-------- C and T change equally; not com- 
| pleted in 60 minutes. 
| Jan. 18 
| 
| 
| | 
| 
” 
So 
| 
| >9,30a.m. 08 | 09 m A and T the same. 
| 10.30a.m. a .18 | A Nee se B red in 40 minutes; T in 26 minutes. 
Ba | 6 | ‘onl 
E08. hi me oe } Sarees | One-third faster on T than on A, 
12.30 p.m. 61 40 40 | 
| 1.30 p.m. | By kt . 63 50 |_--- | A redin 55 minutes; T in 13 minutes. | 
| 2.30 p.m. 43 | .74 | 51 |nneenn= A red in 55 minutes; T in 20 minutes. | 
| 3.30 p.m. | . 53 50 | . 85 | 0.51 | Dred in 45 minutes; T in 13 minutes. | 
= 4380p.m.) — .389 86 «1,021.17 | Dredind7 minutes; Tin 13 minutes. | 
| 5.30 p.m, -14 | 16 12 .41 | Dred in 40 minutes; Tin 18 minutes. | 
Jan. 19 6.30a.m. 10 | 05 | .09 .10 | (These are totals for 13 hours dark- | 
ness). 
| | 
aT—Tree. bSun strikes A at 10.20, B at 10.25, C about 10.40. 
