IV] VARIOUS THEORIES, &c 79 



to make it traverse the wood tangentiall} , but not 

 radially. 



He therefore had cylinders of sap-wood turned, in 

 such a way that the long axis was f i) parallel to a 

 radius of the stem, (2) parallel to a tangent, ie. in a 

 plane at right angles to No, i, and compared their 

 behaviour with (3) cylinders whose axis was parallel 

 to the axis of the stem. The cylinders were all the 

 same size, turned fresh, and kept moist : they were 

 placed on one end of a (J tube, and a solution of eosin 

 driven through by the pressure of mercur}^ in the 

 other leg of the tube. The longitudinal cylinders 

 (3) allowed the eosin to pass with the slightest 

 pressure so long as they w^ere cut from the alburnum 

 — the same cylinders cut out of the duramen were 

 almost impervious. 



The tangential cylinders (2) allowed the eosin to 

 filter through slowly, under a pressure of seventeen cm. 

 of mercury. But not a drop could be forced through 

 the radial cylinders (i) under the same pressure. 

 Even forty cm. of mercury failed to force water 

 through these cylinders. 



This proved that the alburnum transmits water in 

 the tangential direction, but not in the radial direc- 

 tion. Even in the tangential direction, however, the 

 water filters through much more slowly, because, the 



