Water- Conductivity of the Wood in Trees and Shrubs. 241 



Table VII. — Eleven Twigs from Topmost Branches of a large Sycamore 

 Tree blown down in November, 1917. All the twigs had borne flowers. 



Age of 

 twig in years. 



Absolute vol. 

 in c.c. per ^ hour. 



Specific vol. 

 in c.c. per \ hour. 







4 



12-2 



41 -5 



1 



7 -2 



37 -9 



1 



10-2 



34-6 



1 



10 -0 



45-6 



4 



11-5 



47 "5 



3 



8-2 



38 -5 



3 



12 -9 



43 -7 



2 



9-6 



38 -6 



4 



11 -2 



47 -0 



3 



11-4 



48 -0 



3 



11 -0 



47 -5 



Total 

 Avera 



ge • 



470-4 

 =42 -76 



illustrated by the Sycamore. The wood at the base of the shoot always, or 

 almost always, has a lower specific conductivity than that which occurs higher 

 up. The reason lies in the relatively small amount of real vascular, and the 

 large amount of mechanical, non-conducting, tissue. At the same time, the 

 large diameter at the base often causes the absolute volume of transmitted 

 water to be actually larger than that passing through the more efficient (from 

 the standpoint of conductivity) wood higher up in the stem. As the top of 

 the Hazel shoots is approached, both the absolute and the specific conductivity 

 become rapidly reduced, and this is doubtless connected with many of the 

 peculiarities of sympodial growth and branch development near the apex 

 of such shoots, due to the dying back of the apex of the stem, and the 

 subsequent resumption of growth by a lateral branch. The Table (VIII) 

 shows the general type of behaviour of Hazel wands in the respects mentioned 

 above, and it serves to emphasise the similarity that exists between sapling 

 trees and stool-shoots — a similarity that often extends further, and embraces 

 the arrangement and characteristic forms of youth leaves. 



The Ash affords a good example of a tree in which the wood of the sapling 

 and the coppice shoots (" ash plants ") closely resemble each other in respect 

 of their water-conductivity system, and differ greatly in this respect from the 

 ordinary shoots which occur on the branches of the adult tree. For whereas 

 the conductivity is great in the latter, owing to the abundance of wide and 

 long vessels, in the former the character of evergreens is strongly recalled ; 

 even the absolute conductivity is often low in spite of the considerable 

 thickness of the stems, but as branching supervenes, and vigorous secondary 



