64 Rhodora (Marcu 
The dry weight was determined after heating for a while in a steril- 
izing oven at above roo? C. 
The Dendrobium root at the beginning of the test contained water 
to the amount of .36+ oí the root's total weight. In 24 hours ina 
damp laboratory it lost .48+ of the above water. At once thereafter, 
in 46 hours in the damp-box it lost .40 of the water remaining. At 
the end of the test the water left in the root formed .15 of the total 
weight. The Oncidium root had been somewhat dried. Its percen- 
tage of water was then .80+, but it lost water much less rapidly than 
the Dendrobium, the water still retained after 48 hours in the box 
being .79 of the whole weight. In a root of Brassia Wrayae the 
proportion of water had fallen from .78 to .73 of the whole weight 
after 46 hours in the box. 
These figures indicate a very good reason why the roots used have 
no observable condensing power. Even when dry to the touch and 
apparently in condition to absorb vapor they still hold a considerable 
percentage of water. ‘Their state is quite different from that of freshly 
prepared charcoal, for instance, the activity of which in absorbing 
gases is so remarkable. The walls of the velamen of the orchid root 
are already saturated with moisture drawn from the living cells; and in 
the cases under observation draw away and give off so much water that 
the living cells perish. 
Whole plants were used as follows, the first method being that pro- 
posed by Dr. Goodale. 
A young shoot of Dendrobium nobife, bearing two leaves less than 
two inches long, and provided with aérial roots aggregating 28 inches 
in length, was cut from the parent plant, the cut sealed, and the young 
plant left to dry for several days. Medium weight sheet rubber was . 
tied over the mouth of an inverted beaker. Through a puncture the 
transpiring parts of the young Dendrobium were introduced into the 
space thus formed, and the receptacle was made as nearly air-tight as 
possible. While the roots were thus left free, and the shoot was under 
fairly normal conditions, no moisture could escape except from the 
roots. If these condensed vapor the plant and whole apparatus would 
gain weight. Calcium chloride in a test tube had been included along 
with the shoot in order to take up moisture evaporating from the leaves. 
After weighing, this apparatus was set so that the roots of the plant 
hung in a box of the kind before described, the beaker and contained 
shoot being at the same time exposed to the light. A control appara- 
