28 
In my paper, “Ueber den Einfluss von Licht und Temperatur auf den 
Turgor,” '* I showed that in leaves growing or grown in darkness the 
turgor is higher than in normal ones; but the pinna of the coconut which 
I had under observation did not, at least in area, grow during the 
experiment, therefore the explanation in this case must be a different one. 
TRANSPIRATION, 
Three general methods have been used in research on the transpiration 
of plants: First, measuring the water absorbed by the subject of the ex- 
periment; second, determining the loss in weight of the subject and its 
container; third, ascertaining the amount of transpired water after it 
leaves the plant. I have used all of these in my work on the coconut. 
The first method is of the least value because it does not directly meas- 
ure the transpiration, and because the amount absorbed and that given 
off in a given time are not necessarily equal. 1 employed it in some pre- 
liminary experiments only, when my equipment did not permit the use of 
either of the others. As the pinnw which served as subjects always lost 
weight almost from the beginning of the experiments, absorption being 
less rapid than transpiration, the method is inapplicable when any meas- 
ure of accuracy is desired. It will, of course, be understood that all 
ordinary means of keeping the absorption normal were employed. 
In all experiments on the transpiration of this plant in which the 
subject is to be weighed the use of single pinne is practically compulsory, 
for even young seedlings are so heavy that the loss of water from the 
limited leaf area in such time intervals as one hour would escape notice. 
Entire leaves have the same disadvantages as do pinnae, and besides they 
are most unwieldy. When it can be used at all, the determination of 
the loss of weight of subject and container is the most reliable method of 
ascertaining the transpiratory activity of any plant, and when, as in this 
case, the use of whole plants is impracticable, it is usually feasible, with 
proper care and precaution, to be sure that isolated parts of them behave, 
at least for some time, as they would in their natural positions. I have 
used this method in the larger part of my work, but, in contrast to expe- 
rience with other plants, have found it quite impossible to make single, 
isolated pinne of the Cocos maintain the normal rate of transpiration 
for more than a very short time. Leaves cut under water, with the cut 
surface at all times protected from exposure to the air, approximated 
normal transpiration but little if at all more closely than those treated 
without this care. This has repeatedly been my experience. One rather 
extreme illustration will suffice to demonstrate it: The cut surface was 
never exposed to the air. The first weighing was immediately after cut- 
8 Dissertation, Halle, a. S., 1896. 
