The Water Relations of the Pine and the Silver Tree. 
19 
6. The ratio of transpiration to transmission is far higher in the Pine 
than in the Silver Tree. This is shown to indicate that under the experi- 
mental conditions Pine needles exert a greater suction on the water in the 
stem than do Silver Tree leaves. 
7. When transpiration is followed in twigs, as they dry, it is found that 
the Pine twigs at first transpire more rapidly than the Silver Tree twigs. 
After a short time, however, the transpiration of Pine twigs suddenly drops 
and becomes less than that of the Silver Tree twigs. 
8. Determinations of water content show that the Silver Tree leaves have 
a greater water content expressed as a percentage of fresh weight than have 
Pine needles. 
9. The bearing of these results on the water relations of whole trees is 
discussed, and possible interpretations suggested. It is concluded, however, 
that all that can definitely be said at present is that the Pine leaves appear 
to be more resistant to unfavourable conditions than the Silver Tree leaves. 
10. Further lines of research are indicated. 
In conclusion, I should like to take this opportunity of thanking 
Prof. Thoday, at whose suggestion the above work was commenced, for his 
invaluable help and advice throughout the course of the investigation. 
I have also to acknowledge the assistance received from the Union 
Government Research Grant Board, which awarded me a Research Scholar- 
ship, thus enabling me to carry out a very large portion of the work 
described in this paper. 
Eeferences. 
1. Farmer, J. B. — ' Proc. Eoy. Soc./ 90 B, 218-31, 232-50, 1918. 
2. Marloth, E. — 'The Flora of South Africa,' vol. i, p. 145. 
