16 
Transactions of the Royal Society of South Africa. 
experiments show can be exerted by the Pine needles, is a response to the 
structure of the wood, enabling- them to obtain water sufficiently rapidly 
for their requirements. At the same time the much greater tensions, which 
must exist in Pine trees as compared with Silver Trees, probably neutralise 
the greater suction force of the Pine needles, so that the transpiration of 
twigs growing on the tree will probably be less in the case of the Pine than 
of the Silver Tree. Here, however, it must be remembered that we have 
no information as to the maximum tensions which the leaves of either tree 
are capable of exerting or withstanding, and without such information 
inferences as to the behaviour of twigs on the tree are of little value. 
The experiments with drying twigs are suggestive in this connection. 
The figures for these experiments are repeated in the following table, the 
initial fresh weight of the twig being called in each case 100. Alongside is 
given the loss of weight per hour expressed as a percentage of the fresh 
weight, and the original water content per cent, of fresh weight, as 
determined in Experiments 3, 22, 24 : 
Table IV. — Loss of Weight of Drying Twigs. 
Experiments Nos. 20 and 26. 
No. 20: Leucadcndron. 
Time. 
Weight. 
Loss of weight per hour 
per cent, of fresh weight. 
Time. 
Weight. 
Loss of weight per hour 
per cent, of fresh weight. 
9.53 a.m. 
100 
9.57 a.m. 
100 
10.56 „ 
96-12 
37 
10.59 „ 
94-54 
5-3 
11.55 „ 
92-81 
34 
11.58 „ 
89-43 
52 
12.17 p.m. 
9231 
12.22 p.m. 
89-28 
J .16 „ 
90-40 
19 
1.19 „ 
88-82 
0-46 
2.13 „ 
88-82 
1-7 
2.16 „ 
88-45 
0-38 
3.16 „ 
86-90 
1-8 
3.20 „ 
8806 
043 
No. 26 : Pine. 
Experiment No. 33. 
Leucadendron. 
Date. 
Time. 
Weight. 
Loss of weight per 
hour per cent, of 
fresh weight. 
Time. 
Weight. 
Loss of weight per 
hour per cent, of 
fresh weight. 
January 29, 1920 
11.6 a.m. 
100 
11.13 a.m. 
100 
2.4 p.m. 
97-21 
0-95 
2.8 p.m. 
9219 
27 
30 „ 
9.20 a.m. 
84-29 
067 
9.24 a.m. 
87-58 
0-24 
31 „ 
9 50 „ 
6482 
0-80 
9.54 „ 
83-70 
016 
