[VoL. 7 
52 ANNALS OF THE MISSOURI BOTANICAL GARDEN 
Caleiseau Lumber Company, Lake Charles, Louisiana. From 
these samples approximately 250 specimens of each species were 
selected, so that a wide range in resin content and specific 
gravity as well as sap- and heart-wood might be represented. 
The samples were allowed to air-dry for several weeks in a 
room at about 50 per cent relative humidity. They were then 
measured for volume and weighed, and the specific gravity de- 
termined for the whole sample. The samples were usually 
2x6x48 inches. Of course, these specific gravities are not 
standard (Newlin and Wilson, '19), for the specimens were not 
oven-dry when weighed. Since the samples were obtained for 
the purpose of measuring the moisture-absorbing power of the 
wood they were not kiln-dried, for this tends to reduce the 
hygroscopie property of the wood below that obtaining in green 
samples (Tiemann, '07). This point was kindly called to my 
attention by C. H. Teesdale of the Forest Produets Laboratory, 
Madison, Wisconsin, and in a report from that laboratory on 
“Wood in aircraft construction” (1919) the relation of kiln- 
drying of wood to its hygroscopicity is quite generally discussed. 
All samples finally selected for the moisture-absorption tests 
were marked and so labeled that after they were cut into blocks 
2x 2X4 inches, each block could be identified as to which sample 
it belonged and as to its position in the sample. From these 
small blocks uniformly elear pieces were selected for the prepara- 
tion of shavings which were uniform in thickness. A preliminary 
experiment revealed the fact that the moisture-imbibing power 
of wood is not changed by shaving, but that imbibition is more 
rapid than when blocks were used. Therefore, in the experi- 
ments reported below shavings were used. The clear pieces 
selected were of a light color and had a resin content well below 
5 per cent, except those otherwise designated in tables rr and rv. 
Description of humidors.—In order to determine the relation 
between the humidity gradient of the atmosphere and the 
moisture content of wood a closed chamber, or humidor, was 
devised so that a constant temperature would be maintained, 
and so that the humidity could be regulated either by differen t 
concentrations of sulphurie acid in trays enclosed in the cham - 
ber, by varying the evaporating surface of water in trays, or by 
hanging baskets of calcium chloride in the chamber. To pro- 
