Water- Conductivity of the Wood in Trees and Shrubs. 239 



(at whatever the pressure) represents the relative water supply available for 

 them. The apparently unnecessarily large surplus conductivity (absolute) in 

 the lower and leafless parts of the stem is, nevertheless, important, inasmuch 

 as, by lowering the resistance to movement, it enables the full supply to be 

 maintained. 



Table V. — Five Sycamore Sapling Trees cut into Lengths and Tested from 



Base to Apex. 



No. 

 of tree. 



Order of 

 Length.. 



Age in 

 years. 



Absolute Tol. 

 in c.c. per 5 hour. 



Specific vol. 

 in c.c. per i hour. 



Average 

 of specific vol. 

 per tree. 



D 

 E 



basal 



3 



18 -8 



29 -0 



2 



2 



24-6 



42 -0 



3 



2 



17 -6 



38-0 



apical 



1 



6-8 



38 -3 



basal 



2 



21 -0 



27 -0 



2 



2 



21 -8 



35 -5 



8 



1 



17 -4 



37 -4 



apical 



1 



6-8 



17 -0* 



basal 



2 



15-6 



40-3 



2 



2 



12-4 



48 -0 



3 



1 



4-2 



33 -0 



apical 



1 



1 -3 



26 -5 



basal 



3 



16 -6 



31 -7 



2 



2 



16 -6 



32 -0 



apical 



1 



11 -6 



46 -0 



basal 



2 



15-4 



39 -5 



2 



1 



11-2 



42 -5 



apical 



1 



4-4 



41 -5 



36 -95 

 29-22 



29-22 



36-57 

 41-17 



The general average of the specific volumes given in the last column = 34 -63 ; all but one of 

 the five sets of averages fall ■within ± 5 '5 of this number. 



* This apex contained immature wood, hence its exceptionally low value. 



The slightly lower specific conductivity observed at the base finds an 

 explanation in the circumstance that a relatively larger proportion of the 

 whole wood in this region is modified to subserve mechanical requirements at 

 the expense of its water-conducting function. The same thing also occurs, 

 but to a very much larger extent, in the stems of young climbing plants 

 during the period that elapses between germination and the formation of the 

 foliage-bearing shoots. It is, of course, difficult to decide as to which is cause 

 and which is effect in tliese cases, but it appears likely that the relatively 

 ill-conducting wood which is first formed, both in climbers and in many trees, 

 encourages the rapid upward growth of the shoot by stopping down exuberant 

 leaf production and reducing the tendency to early lateral branching. The 

 higher absolute conductivity noticed at the base of the young sycamore trees 

 is largely due to the quality of the secondary wood, in which water- 

 conducting tissue is more abundant. But the steadiness of the figures 



