2 53 
Groom.—Remarks on the Oecology of Coniferae. 
But apart from the positive results demonstrating the rapid rate of the 
transpiration current in the larch, we are not justified in the assumption 
that there is a universal and direct proportion between the habitual or 
maximum rate of transpiration of leaves and the calibre of vessels or 
tracheides. And it may be remarked here that Ewart’s experiments, so far 
as they register rates of flow under the influence of transpiration, merely 
record the rate at which the eosin ascended, and the approximate rate at 
which the water ascended, under the conditions of transpiration then 
prevailing; but they do not record the rate at which water could easily 
ascend under a higher rate of transpiration, nor do they demonstrate that 
there is any universal rule that the calibre of the wood vessels is directly 
proportional to the rapidity of the transpiration current of a tree. It is true 
that in climbing plants where the transpiration current is known to be very 
rapid, the tracheae are notoriously wide. Ambronn and Westermaier 
explain this as an expression of the principle that the resistance to the 
travelling of water up tubes decreases with increase of diameter of these. 
Decrease or increase in diameter of the conducting tubes is only one of 
several possible arrangements to decrease or increase the transpiration 
current. 
Von Hohnel’s prolonged experiments supply us with statistics for 
comparing the rate of transpiration and the width of the vessels. 
In the subjoined table the first column gives the name of the tree. 
The second and third represent the number of grammes of water transpired 
in 1878 (June to November) and in 1879 (April to November) per gramme 
dry weight of leaf. The fourth and fifth columns record my calculations of 
the rate of transpiration per square centimetre during the same periods. 
The sixth and seventh columns record the maximum rates of transpiration 
(in the months of June, July, or August, 1879) attained, reckoned re¬ 
spectively per gramme dry weight and per square centimetre of leaf- 
surface. The eighth column gives the calibre attained by the wood vessels. 
Per gramme 
weight. 
Per sq. cm. 
Per grm. 
weight 
maxim. 
Per sq. 
cm. 
maxim. 
7 nm. 
Calibre. 
1878. 
1879. 
1878. 
1879. 
Betula alba .... 
67.9 
84-5 
2.7 
3*36 
23.1 
0.85 
0.1-0.131 
Fraxinus excelsior 
56*7 
98-3 
1.9 
3.26 
25.8 
i-i 
0.2 
Fagus sylvatica . . 
47.2 
85*9 
i *3 
2.4 
55*3 
2-2 
0.057-0-076 
Acer Pseudoplatanus . 
43*6 
61.8 
i *4 
2 
24.7 
O.67 
0.1 
Carpinus Bet ulus. 
56-2 
75-9 
1.2 
i-6 
24*3 
0-25 
0.057 
Quercus Cerris . . 
25 
61-4 
1 
i *7 
20.5 
O.77 
(o- 35 ) 
Acerplatanoides . 
46 
5 i -7 
1 
1.17 
I2-I 
O.27 
0*07 
Quercus Robur . . 
28.3 
66-2 
0-83 
i *9 
11.23 
O.79 
o* 2 5 (" 3 * 5 ) 
The figures giving the dimensions of the vessels are from Pedersen’s 
pamphlet, except in the case of Quercus Cerris , which I measured. 
