310 BOTANICAL GAZETTE [APRIL 
to 10:00 A.M. This difference is ascribed to the more rapid utiliza- 
tion of the reserve water which is stored up in the leaves and trans- 
locating system of the plant during the night. Thus on the dunes, 
where the reserve is utilized more rapidly than it is restored by 
absorption and translocation, there will occur a depression in the 
index later in the day. On the clay soils, the rise being slower, 
frequently the reserve is not utilized until midday; hence there 
occurs a lower maximum and a much less noticeable saturation 
deficit, or none at all. This means that the maxima of tempera- 
ture, relative humidity, and evaporation concur in time or more 
nearly approximate doing so than for the dune series. ‘The closest 
approximation to this.concurrence on the sands was recorded for 
cloudy days with low temperature and evaporation and a high 
relative humidity. All these conditions of environment are tend- 
encies toward the prevailing condition in the forest, in contrast 
with those characterizing open dune situations. 
3.. The transpiration stream shows a simple curve for readings 
taken on forested clays, rising gradually to a maximum at noon 
and falling at approximately the same rate to the night level. 
4. The effect of thunder showers is recorded in a sharp reduc- 
tion in the transpiration index. Frequently when the precipitation 
occurs in the early afternoon there is a second rise in the tran- 
spiration curve to a level in excess of the normal rate for that time, 
probably owing to the accumulation of a slight reserve, while the 
transpiration rate is lower than that of absorption. 
5. Partial abscission produces an effect not unlike that found 
accompanying the development of a wilting coefficient. Under 
these circumstances there is a low morning rise which quite early 
reaches a maximum, and is followed by a rapid decline accompanied 
by the closure of stomata and visible wilting, the transpiration 
falling until it becomes almost entirely cuticular. The morning 
rise takes place in this instance because of the slight water reserve 
accumulated during the night. 
_ 6. A wilting coefficient did not develop in any of the clay soils, 
and there was always a considerable amount of growth water 
available, but its occurrence on the sand series produced an effect 
closely similar to that occasioned by abscission. 
