134 : BOTANICAL GAZETTE [AUGUST 
streams, while, when conditions require, they provide, by an 
automatic change, a rigid support to the tensile sap and oppose 
an impermeable barrier to undissolved gas.” 
In studying the fundamental factors which control the penetra- 
tion of preservatives into green and seasoned timber, the writer® 
_ 
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Fic 1.—A, piece of radial wall of a tracheid, showing a bordered pit in surface 
view; on the left, part of the dark colored torus, or thickened portion of pit membrane, 
may be seen through the oriface in the embossed secondary wall; on the right, part of 
this overlying wall has been removed, exposing a surface view of the forus and per- 
forated membrane; B, view of section a—b through bordered pit, showing embossed over- 
lying and underlying secondary walls (Br), torus (Ts), and membrane (Me); G, view of 
section a’—b’, showing how the torus acts as a valve by taking the positions Ts’ or Ts”. 
has had occasion to analyze critically the data upon which these 
conclusions in regard to the structure and function of the pit 
membranes are based. 
3 Bartey, I. W., The validity of certain theories concerning the penetration of 
gases and preservatives into seasoned wood. For. Quart. 11:5-11. 1913. 
, The structure of the pit membranes in the tracheids of conifers, and its © 
relation to the penetration of gases, liquids, and finely divided solids into green and 
seasoned wood. For. Quart. 11:12-20. 1913. 
