The Water-Conductivity of the Wood in Trees and Shrubs. 219 



tissues in the wood wliich materially determine the nature and commercial 

 value of timber. 



The method adopted for securing the data required for the present investi- 

 gation consists essentially in measuring the amount of water passing in a 

 given time and at standard pressure through a definite length of twig or 

 branch, the cross-sectional area of whose wood is carefully ascertained. From 

 the data thus obtained, it is easy to state the result in terms of the amount 

 of water that would pass under precisely similar conditions through a stem, 

 the cross-sectional area of the wood of which measured 1 sq. cm. iu cross- 

 section ; in other words, starting from a ratio, " absolute volume " -r- observed 

 area of wood, to state the results in such a form that " area " shall equal 

 1 sq. cm. The actual procedure adopted was as follows : — 



A branch of a tree or shrub is immersed in and severed under water, in 

 order to obviate the entrance of air into the vessels. Twigs from | to 1 cm. 

 in diameter are cut off, also under water, and are divided into lengths of 

 exactly 15 cm. In the case of rod-like branches, e.g., of sapling trees or 

 coppice-shoots, it is possible to get from three to five or more lengths, and 

 these are kept together and numbered from base to apex for purposes of 

 subsequent identification. Any lesions consequent on trimming off side 

 branches are well luted up with sealing-wax of low melting point, this 

 proving the best of all the substances tried. The twigs are then put into a 

 vessel of boiled water and subjected to vacuum treatment, in order to free 

 the wood as far as possible of any air it might contain. This precaution has 

 served to eliminate most of the discrepancies which appeared in the earlier 

 stages of the investigation. The twigs are then fixed (wiring them if neces- 

 sary) by their lower or basal ends into the pressure tubing at the ends of the 

 vertical tubes below J, J2, J3, J4, in the apparatus shown iu fig. 1, and the 

 amount of water, delivered at a pressure of 30 cm. of mercury, which is 

 transmitted in exactly 15 minutes, can easily be collected and measured in 

 the graduated glasses below. Three or four successive measurements were 

 made for each twig in order to test the uniformity of flow, which thus lasted 

 for about an hour or more. Only those results which showed no, or very 

 small, deviations were accepted, but the number of those discarded as 

 untrustworthy becomes very trifling when precaution is taken to prevent air 

 trouble. Stems which contain resin or mucilage, however, are apt to be 

 unsatisfactory, owing to the blocking of the ends of the water-conducting 

 tracts. After the stems are removed and the estimation of the transmitted 

 water is finished, the cross-sectional area of the wood is measured. The twig 

 is bisected transversely, and a section from the surface so exposed is prepared 

 for the microscope. The limits of the wood are accurately traced on paper by 



T 2 



