1920] 
ZELLER—IMBIBITION BY WOOD AND SPORE GERMINATION 55 
be measured experimentally samples were chosen and analyzed 
by the method previously reported (Zeller, '17). 
RESULTS OF EXPERIMENTS ON MOISTURE ABSORPTION 
The data from the experiments to show the relation between 
the relative humidity of the atmosphere and the moisture con- 
tent both of sap- and heart-wood of shortleaf and longleaf pine 
are given in tables 1, 11, 111, and rv. 
From the data recorded in these four tables (1, 11, 111, and Iv), 
the humidity-moisture curves shown in figs. 1, 2, 3, and 4, 
respectively, were plotted. These curves represent the ulti- 
mate moisture content at a given temperature and relative hu- 
midity of the surrounding atmosphere. The samples used in 
each experiment were of three distinct specific gravities chosen 
to represent the approximate average specific gravity of the 
species of wood, as well as densities both heavier and lighter 
than the average. In the case of heart-wood, however, an extra 
series of samples was used. These were highly resinous and 
consequently very dense. Other than these highly resinous 
pieces, the samples had a resin content well below 5 per cent. 
The four curves are strikingly similar. In all cases where the 
samples of wood represented have specific gravities lying be- 
tween .41 and .75 to .80 and small percentages of resin, the 
general curve for the moisture absorbed is followed up to a cer- 
tain relative humidity where the percentage of moisture taken 
up by the wood of the three densities begins to vary according 
to the density. The lighter, or less dense, samples, from this 
point, take up more moisture with increased atmospheric hu- 
midity than do the denser samples. This occurs at a relative 
humidity averaging from 94.75 to 96 per cent. There seems to 
be but one explanation for a divergence of the curves at this 
juncture. Up to this point the wood fibre has not received 
enough moisture from the atmospheric humidity to satisfy its 
imbibition capacity, but beyond this point this hydration capac- 
ity is over-satisfied and the moisture over and above that ab- 
sorbed by the fibre is adsorbed by the surfaces exposed. If this 
theory is correct the point of divergence of the three moisture- 
humidity curves represents the fibre-saturation point. As an 
irreversible colloid, wood is undoubtedly limited in further 
