Water in Trees lender Australian Conditions. 95 
The following observations on Acacia show that a single vessel may 
run nearly the whole length of the tree, while less than 1 per cent, ran for 
one-third, and not more than 5 per cent, for one-fifth the length of the 
main stem. The vessels in the branches are usually smaller and shorter 
than in the main axis, and they are more numerous per sq. centimetre in 
the wood on young stems than in that on older ones. Not only are the 
longest vessels found in the main axis but they do not appear to run into 
branches to any extent, and the same applies to the branches themselves ; 
the longest vessels on a main axis do not as a rule run into secondary 
branches. Hence the number of partition walls in the path of a particular 
line of sap-flow will always be greater than the number of branchings it 
passes, and as regards the resistance to flow, this will put a young branch 
at the top of a tree on a greater equality with the twigs on a basal branch 
than would otherwise be the case. 
Mercury Method. 
Acacia mollissima: 
I. 
Age. 
Diameter 
Position of 
Length of 
Diameter of 
Average 
Diameter 
of vessels. 
at base. 
longest vessel. 
longest vessel. 
largest vessel. 
0) 
Full tree 
6 yrs. 
3.5 cm. 
New wood 
200 cm., 
•131 mm. 
.101 mm. 
Height 2 *44 m. 
5 vessels at 134 cm., 
also one in proto- 
xylem at 170 cm. 
3rdyr’s. wood 
(exceptional) 
(*) 
Root and 
6 yrs. 
33 cm., 3 vessels at 
hypocotyl 
25 cm. 
•065 mm. 
(0 
Branch of same 
3 yrs. 
1*3 cm. 
New wood 
102*5, 5 vessels at 
.104 mm. 
70 cm. 
II. 
Full tree 
3 yrs. 
6-2 cm. 
New wood 
240 cm., 60 vessels 
.13 mm. 
•09 mm. 
rk ( a ) 
Forked trunk 
at 95 cm. 
Height 4-5 m. 
Mercury method 
Average no. of vessels at tip 1 (21 per sq. mm.), 1336 
Fork ( 6 ) 
Height 3-94 m. 
(Air pressure) 
3 yrs. 6 cm. In new wood, 213 cm. (2 vessels), 
one in spring 8 vessels at 125 cm. 
and one in 
autumn wood 
Average no. of vessels at tip (30 per sq. mm.), 1500 
.09 mm. 
.07 mm. 
(0 
Branch of same 
Length 94 cms. 
2 yrs. i*4 cm. New wood 3 vessels at 94 cm., 
6 vessels at 6 cm. 
Average no. of vessels at tip (38 per sq. mm.), 665 
.08 mm. 
.05 mm. 
(<0 
Branch of same 
Length 1-48 m. 
3 yrs. 2.1 cm. New wood 115 cm., 38 vessels 
at 28 cm. 
Average no. of vessels at tip (26 per sq. mm.), 735 
• 1 mm. 
.07 mm. 
d) 
Branch of same 
Length 1-21 m. 
2 yrs. i-3 cm. 119 cm., 18 vessels 
at 37 cm. 
Average no. of vessels at tip (42 per sq. mm.), 1188 
.1 mm. 
.06 mm. 
1 Tip = where the longest vessel ends. 
