1920] 
ZELLER—IMBIBITION BY WOOD AND SPORE GERMINATION 53 
duce the higher humidities, curtains of absorbent paper were 
hung in the chamber so that the lower portions were in contact 
with water in trays. This increase in evaporating surface 
proved very effective. 
The humidor with apparatus complete as we used it is shown 
in plate 1. The humidor proper consists of two double-walled 
boxes, one within the other, built of spruce lumber. The 
double walls are packed with sawdust for insulation against 
temperature changes. For added insulation there is an air space 
separating the inner and outer box. The inner box, which is 
the chamber proper, has a double-walled door provided with a 
double-glass window, through which temperature and dew- 
point observations can be made without opening. The outer 
door is double-walled and packed with sawdust. The doors are 
provided with ordinary cold-storage catches. There are three 
one-inch openings, one through the top and one through each 
end. The inner walls of the humidor chambers were water- 
proofed in two ways: (1) Those of two humidors were brushed 
with hot paraffin (parawax) and were then thoroughly ironed 
with a hot electric iron. Further applications of the paraffin 
were made in the same manner. (2) The walls of two other 
humidors were primed and painted with several coats of a 
water-proof enamel and valspar. The paraffin treatment does 
not give as good an appearance as the enamel paints, but it 
proved to be the better water-proofing agent. 
The temperature of the chamber was maintained at 25° C. by 
means of a bimetallic thermo-regulator in circuit with an electric 
light as a heating element. 
Determination of relative humidity.—There was no difficulty 
in maintaining a constant relative humidity throughout any one 
experiment. "The relative humidity of the chamber was deter- 
mined by means of a Milliken dew-point apparatus, which 
consists of a highly polished, nickel, cylindrical cup provided 
with a three-hole stopper. One of these holes supports a 
thermometer and the other two provide an intake and outlet 
for the siphoning of water or freezing mixtures through the cup. 
This apparatus shows plainly in fig. 2, pl. 1. The dew-point is 
determined by the appearance and disappearance of the film of 
moisture on the polished cup as the temperature is changed by 
