492 
WALTER L. C. MUENSCHER 
In order to prevent the warm paraffin from doing any possible injury 
to the stem of the plants partially cooled strips of paraffin were first 
wrapped around each stem at the surface of the soil where the hot 
paraffin would otherwise come in contact with the stem. Each jar 
was marked by writing a number on the paraffin surface. 
After the jars had been continued for several weeks the paraffin 
began to draw away from the edges of the jar slightly. In order to 
determine any possible error due to evaporation from the edge of the 
jar a number of jars were reweighed several times after the plants 
had been removed to see whether any water was lost by evaporation, 
but this was found to be very small or sometimes so small that it 
could not be detected by weighing from day to day. After removing 
the paraffin from the jars I found that it had run down between the 
edge of the soil and the stone crock several centimeters and still 
formed a very tight seal near the surface of the soil so that very little 
water could escape. 
3. The Determination of Water Loss 
A week after the jars had been sealed I took the first weighing for 
determining the amount of water lost. The amount of water lost 
was computed from the decrease in the weight of the jar between the 
intervals of weighing. At first the jars were weighed twice daily, 
between six and seven o'clock A. M. and between six and seven o'clock 
P. M. Later the weighings were taken only once each day in the 
evening, while some of the final weighings were taken at intervals of 
two or three days; but the jars were always weighed between six and 
seven o'clock P. M. For weighing I used a ''micrometer scale" 
which has a capacity of 18,000 grams and weighs very accurately 
down to two or three grams. 
The loss of water from the jar was replenished at intervals of 
two or three days through the glass tube which was inserted for that 
purpose. The amount of water added at one time was approximately 
the amount that was lost by the plants during the interval since the 
last addition of water, and was added in the evening between seven 
and nine o'clock. 
4. The Determination of Leaf Areas 
Numerous methods have been employed from time to time for 
the determination of leaf areas, but it was found impracticable to use 
