316 BOTANICAL GAZETTE [OCTOBER 
Professor B. E. LivrncstTon, an attempt was made to obtain further 
information concerning the march of the wilting process by means 
of cobalt chloride paper and the index of foliar transpiring power. 
Various writers have shown that the transpiration rate falls 
suddenly with wilting, but rises again thereafter to a considerable 
extent, subsequently to fall once more as desiccation finally occurs. 
It appeared that these alterations in the transpiration rate must be 
due to internal conditions (within the plant), and that a similar 
march should be shown by the value of the index of transpiring 
power. To test this supposition, sunflower plants (Helianthus 
annuus L.) were lifted from the open soil in the forenoon, the adher- 
ing soil was shaken from the root system, and the plants were 
allowed to wilt in the laboratory. The temperature of the room 
was about 32°C. and varied but little during the experiments. 
Determinations of the index of transpiring power for both the 
upper and lower leaf surfaces were made at hourly intervals, the 
first determination just preceding the lifting of the plant. 
An example of the sort of results obtained is given in table I. 
Five leaves of different ages were employed, the same leaves being 
tested at each time of observation. Although there were con- 
siderable differences in the indices for different leaves at any one 
time, according to their various ages or positions upon the plant, 
all five indices have been averaged to give a single index for each 
time. The first observation was made just before the plant was 
lifted from the soil. No wilting was apparent at this time. The 
last observation was made after drying of the leaves became pro- 
nounced. It required 10-15 minutes to complete each observation, 
the tests being begun at the time indicated in the table. 
From the data given in table I it is at once clear that the indi- 
ces first decrease rapidly, then increase, and then decrease again. 
This march for the upper and lower surfaces is shown graphically 
in fig. 1, where abscissas denote time and ordinates denote index 
values which are shown upon the graphs. 
Wilting began almost immediately after the removal of the 
plant from the soil. The indices are seen to decrease very rapidly — 
during the first hour. This first rapid decrease is followed by @ 
continued but very gradual decrease during the four following 
