The Water Relations of the Pine and the Silver Tree. 
9 
Comparison of the leaf area measured in this way with the area calcu- 
lated from — 
Length of leaf x Total perimeter of mid- section 
showed that the latter was always slightly greater than the former, e. g. — 
b. 
No. Area from graph. Mid-s^n^Tength. a P er cent of h ' 
1 7'08 sq. cm. . 7 38 sq. cm. . 959 per cent. 
2 . 6-75 „ . 7-10 „ . 95-1 
3 3-39 „ . 3-48 „ . 974 
The actual leaf area was therefore taken to be 96 per cent, of the area 
calculated from the expression, perimeter of mid-section x length. 
To obtain the total leaf area of a twig, the leaves were arranged in 
groups according to their length, and the diameter of the flat surface of 
representative leaves from each group measured. The leaf area of each 
group was then obtained from the expression, number of leaves x length x 
diam. mid-section x 2 - 8 x 0 - 96. As already explained, 2*8 is the value of 
(C/D + 1) and 0-96 represents the necessary reduction to 96 per cent., just 
mentioned. 
The total leaf area of the twig was then obtained by adding together the 
areas of the groups. 
III. EESULfS. 
A. The water-conducting power of the wood. — The first experiments were 
confined to measurements of the conductivity of the wood of the two trees, 
and showed a considerable difference between the two. It should be noted 
that the " conductivity " in these experiments differs from Farmer's 
" specific conductivity.' 1 The former is calculated for a pressure of 186 cm. 
of water, the latter for a pressure of 30 cm. of mercury. At the outset a 
few measurements were made of the conductivity of the wood of the Oak as 
well as of that of the Pine and Silver Tree. The results obtained for these 
three trees are in accordance with Farmer's main conclusion that evergreens 
possess wood of markedly lower efficiency than that of the broad-leaved 
deciduous trees, and that the absolute range of variation in individual 
species is far narrower than in deciduous forms. 
In the few measurements made of the conductivity of the wood of the 
Oak the values ranged from 18 9 to 107*8, the average of seven experiments 
being 46*6. 
Of the three trees the Pine showed least variation in its conductivity. 
For the six preliminary measurements with Pine wood the average conduc- 
tivity was 7*1, the values ranging from 5'9 to 8 2. These measurements 
were made in July, 1919; in January, 1920, further measurements were 
