Water-Conductivity of the Wood in Trees and Shrubs. 237 



Table III. — Twenty-seven Birch Twigs, Lateral Branches. 



Age in 



Area in inches 



Absolute vol. per 



Specific vol. per 



years. 



( X 10). 



\ hour. 



i hour. 



2 



2-34 



8-2 



54-0 



1 



1 -90 



6 -4 



52 -3 



1 



2-30 



5-0 



33 -5 



1 



2-10 



.7-2 



53 -0 



2 



2-95 



10 -0 



52 -5 



1 



2-17 



6-9 



49-0 



2 



2-44 



9-2 



58 



2 



2-46 



8-2 



52 -0 



1 



2-53 



8-4 



51-5 



2 



2-90 



7-0 



37 -5 



1 



2-78 



7-2 



40 -0 



2 



2-60 



7 -0 



47-7 



1 



1 -64 



5-8 



55 -0 



2 



1 -76 



5-9 



51 -8 



1 



1 -30 



3-4 



40 -5 



1 



1-90 



7-1 



58 -0 



1 



1-80 



5-2 



55 -0 



2 



1 -87 



5 -0 



41 -5 



2 



1 -60 



5-0 



48-5 



2 



2-54 



8-8 



53 -5 



2 



1 -40 



3-6 



40-0 



2 



2-22 



5-7 



39 -8 



2 



2-06 



3-6 



28-0 



9 



3 '42 



12 '8 



Oo \J 



2 



2-57 



12 -0 



73 -0 



2 



1 -50 



4-0 



41 -3 



2 



1 -30 



4-8 



57-0 





58-35 ins. 



184 -4 



1311 -9 





(at X 10) 

 = 3 "76 sq. cm. 



actual size 



184-4 



— 49... 



3-76 







average — 48 -6 



As another instance of variation, it will be convenient next to consider the 

 behaviour of young sapling trees, as compared with that of the branches and 

 terminal twigs of an adult individual belonging to the same species. 



The Sycamore furnishes a good example, and I have found the same condi- 

 tions that exist in it to apply more or less entirely to all other trees I have 

 been able to examine. If well grown young trees of from four to five years 

 of age be cut up and tested from base to apex, it becomes apparent that the 

 wood in the upper (younger) part of the vertically growing stem is a better 

 conductor of water per unit area than that nearer the base. But although 

 the specific conductivity shows relatively little change, there is a great falling 

 off in the amount of water absolutely transmitted, owing to the narrowing of 

 the diameter of the stem towards the apex. This becomes intelligible when 

 one reflects that saplings, until they begin to branch, commonly possess a 

 relatively small leaf surface. The absolute amount of water transmissible 



