34 TRANSPIRATION IN A DESERT PERENNIAL. 
OBSERVATIONS ON TRANSPIRATION EXPERIMENTS. 
1. The 18 relative transpiration curves taken in the sun all show a maxi- 
mum earlier in the day than the time of maximum evaporation. 
2. All of therelative transpiration curves, except those from experiments 
I, II, VI, and a part of TX, show an abrupt drop after the maximum, 
followed by a rise which appears sometimes an hour earlier than the time 
of maximum evaporation and sometimes coincident with it, but never later. 
1a. An early maximum in actual transpiration corresponding to that 
of the relative transpiration appears in all of the plants growing in the open, 
except those in experiments I and II. In the case of potted plants this 
maximum behaves somewhat irregularly. In experiment VI it is not pro- 
nounced, in VII it is lower than a second maximum, in IX it fails to appear 
in the case of three hot-house-grown plants and appears as a secondary 
maximum in the case of the transplanted seedling. 
2a. All curves of actual transpiration of plants growing in the open, 
with the exception of I and II, show a drop and rise in the morning. As 
in the case of the relative curves, the potted plants differ among themselves. 
Experiment VI shows the drop and rise to a small extent; IX shows a 
flattening of the slope in the morning followed by an increase in the angle 
of slope in the three hot-house plants and a drop followed by a rise for the 
transplanted seedling; X shows straight lines followed by a rise at the time 
of the drop in the relative transpiration. 
3. It will be seen from table 14 that leafless seedlings and leafless branches 
of adult trees give the same average for maximum relative transpiration 
for the day, and that this average is lower than the average maximum for 
branches in leaf, and this is in turn much lower than the average maximum 
for potted plants. The one seedling which was transplanted from the open 
shows a maximum somewhat under the maximum average of branches in 
leaf, but is higher than two of the individual maxima of which the average 
is made up. 
4. The differences in anatomical features shown in the sections in figure 1 
indicate that the same relation exists between the water-losing power 
in leaves as compared to stems and in green-house plants as compared to 
those grown in the open, as is shown in the preceding paragraph. 
5. Experiment X shows that a change of soil moisture in one potted plant 
from 15.1 per cent to 3.5 per cent, 7. ¢., a lowering of 76.8 per cent, was accom- 
panied by a lowering of 98.4 per cent of the original amount of relative 
transpiration; in a second plant a change of the soil moisture from 14.5 to 
3.4 per cent, ¢. ¢., a lowering of 76.6 per cent, was accompanied by a lowering 
of 97.2 per cent of the original relative transpiration. In only one case 
were valid readings of soil moisture, at a depth of 30 cm., taken at times 
corresponding to transpiration readings from trees, and this shows that a 
change in soil moisture from 14.0 per cent on March 27 to 32.0 per cent 
on August 22, 7. e., an increase of 128 per cent, was accompanied by a 
change in relative transpiration from 0.181 on March 27 to 0.302 on August 
22, 7. e., an increase of 72.3 per cent. 
