298 | BOTANICAL GAZETTE [APRIL 
in the morning, reaching a maximum early (8:00-10:00 A.M.), after 
which there is a gradual closing until dark, about which time they 
approximate the closed night condition. During the day it seems 
that the maximum water loss is always less than the maximum 
amount which may be diffused from the open stomata, so that the 
lower general average for certain days must be referred to other 
causes. 
On the sand dunes there is a strong tendency to high transpira- 
tion, as is evidenced by the graph representing station D for Septem- 
ber 2 (1, fig. 8). The evaporation and relative humidity in this 
instance were closely similar to that recorded for station N (fig. 3). 
The temperature, which registered the greatest degree of difference, 
averaged about 4 per cent higher, yet the transpiration index was 
just roo per cent greater, averaging o. 23 in the latter instance and 
0.46 inthe former. Thus in any given situation the transpiration 
may be high or low irrespective of the relative humidity, tempera- 
ture, and evaporation, although these factors are certainly instru- 
mental in influencing fluctuations in the transpiration stream. In 
other words, Tilia on the open dunes will transpire more actively 
than the same species in the mesophytic forest, irrespective of 
atmospheric conditions; and, with similar weather conditions pre- 
vailing, in clay environments there may be a considerable variation 
in the transpiration index from day to day. It is the opinion of 
the writer that the former of these conditions may be associated 
with structural differences, and investigations are being made with 
the hope of giving further light upon this phase of the problem. 
GROWTH WATER.—The relation of growth water to the tran- . 
spiration index has proved interesting. This is the soil moisture 
content minus the wilting coefficient as expressed by FULLER (3). 
Fig. 7 illustrates the relation between growth water and transpira- 
tion as recorded in the field during the course of investigation. 
The five stations located on the dune sands are represented by 
A, B,C, D,and E. It willbe noted that the growth water is very 
low, ranging from an average of 1.25 to 2.60 per cent. Further- 
more, the water loss by transpiration is found to be greatest at 
the most exposed station, where the growth water average is lowest, 
and decreases rapidly to a level, whichis found at stations A and B 
