1916] BAILEY—ASCENT OF SAP 139 
from these figures seemed probable, since sap is not pure water, the 
membranes are elastic, the openings are not perfectly circular in 
most cases, and the formula is of questionable value in dealing with 
holes of such minute radii. 
In order to check the matter experimentally, a series of tests 
were made to determine what pressure is required to force air 
through the membranes of conifers when they are saturated with 
sap, distilled water, glycerine, acetic acid, acetone, ethyl alcohol, 
and other liquids of varying surface tensions. A hemlock (Tsuga 
canadensis) 85 feet and a larch (Larix laricina) 60 feet in height 
were felled, and pieces of sap wood including the last formed layers 
were removed at various points along the stem. These speci- 
mens were cut (under water) into small cylinders and carefully 
tested to determine the location of tracheids which contained bubbles 
of air or gas.. Microscopic examination of the material showed that, 
at the season when the wood was cut (November), very few of 
the tracheids of the last formed layers of growth of hemlock and 
larch contained bubbles of air or gas. Those tracheids which con- 
tained gas were conspicuous, owing to their lighter color, and 
their presence could be demonstrated, in cylinders of sap wood 
used for experimental purposes, by allowing a dilute solution of 
India ink to pass through the specimens. The ink traveled very 
rapidly in those elements that were filled with water, and compara- 
tively slowly, or not at all, in cells which contained bubbles of gas. 
In determining the pressures required to overcome the surface 
tension of the liquids in the perforations of the pit membranes, 
those pressures were recorded at which air succeeded in penetrating 
all of the water-filled tracheids.’ As might be expected from the 
variation in the size of the perforations, the air penetrated many 
tracheids before these pressures were attain 
After testing a specimen with alcohol, sci acid, acetone, 
etc., it was washed clean, thoroughly re-soaked with distilled water, 
and, retested in order to determine whether the membranes had 
remained unaffected by the liquids. 
7 That the air which passed through the specimens did not travel in intercellular 
Spaces was determined in two ways: by direct observation with a binocular micro- 
Scope, and by the fact that the lumens of the tracheids, which at the beginning of the 
tests were filled with liquid, contained air at the end of the experiments. 
