274 : BOTANICAL GAZETTE [aPRie 
The leaves with their decurrent wings were first cut from each 
plant and weighed immediately. Thereupon, prints for determin- 
ing the leaf area were made on blue-print paper. The stems, 
including the inflorescence, were cut off at the surface of the ground, 
weighed, and cut into small pieces for drying. In order to obtain 
the roots, the soil was washed out of the tanks with a stream of 
water. With the aid of a brush the roots were washed free from - 
adhering soil particles. They were then dried by being pressed 
between towels and absorbent paper, weighed, and cut up for 
To obtain the weight of dry substance, the fresh material was 
dried at 60-70° C. and ground in a drug mill with the observance 
of such precautions that the material was quantitatively recovered. 
The leaves, stems, and roots of each plant were ground separately. 
The air-dry material thus obtained was weighed, and from each 
lot four samples of approximately 2 grams each were taken. These 
were dried to a constant weight in a slow current of hydrogen at a 
pressure of 6 cm. of mercury and a temperature of 78° C. 
In order to make a comparison of the transpiration per unit area 
of leaf surface for the plants in the two stations, the leaf prints made 
at the time of harvesting were cut out and weighed, and their area 
was calculated from the relation of their weight to the weight and 
total area of the original paper. As a basis for calculating the 
transpiration per unit area of leaf surface, the average quantity of 
water transpired during the last five days of the experiment was 
taken. Since the plants had reached the flowering stage, it may 
be assumed that there was very little change of area of the leaves 
during this period. The taking of the average daily transpiration 
obviated to a certain extent peculiarities which might be exhibited 
by the transpiration of a single day. 
Data 
In connection with the presentation of the data, attention may 
again be called to the fact that the plants used in these experiments 
were the descendants of a single self-fertilized mother plant whose 
progeny was shown by subsequent cultivation during two genet 
tions to be of a pure strain. For this reason more confidence ae 
