245 
Groom.—Remarks on the Oecology of Coniferae. 
piration per square centimetre the evergreen Conifers are seen to transpire 
very slowly, whereas the larch transpires at a rate equalling that of rapidly 
transpiring deciduous dicotyledons. This is demonstrated by statistics 
concerning Von Hohnel’s second series of experiments conducted during 
1879-80 as shown below. 
In these experiments, as in the earlier ones by Von Hohnel, great 
differences showed themselves in the rate of transpiration even of the same 
species and in the same situation. These particular differences, I think, must 
have been due to differences in the amount of water supplied, as the grave 
defect of the pot-method of measuring transpiration is that the rate of 
transpiration is so largely determined by the amount of water supplied 
to the roots. Moreover parsimonious watering leads to a shedding of the 
leaves and a further decrease in the apparent rate of transpiration. Hence, 
to show indubitably the rapid expenditure of water by the larch-needles, 
I compared their rate of transpiration with the maximum rate attained 
by dicotylous trees. 
The subjoined statistics are derived from my calculations based upon 
Von Hohnel’s results, and they record the approximate maximum trans¬ 
piration in grammes per square centimetre during the year 1879-80. 
Fagus sylvatica 
Larix decidua 
Quercus Cerr is 
Betula alba ... 
Carpinus Betulus 
2.5 
(Larix decidua in half shade 1-4.) 
In reference to these results, I note the maximum shown by the beech 
was attained in the smallest specimen, so that it is probable that the high 
result was due to high rate of watering. Two numbers are given in 
connexion with the larch exposed to light, because the air-dry weight 
of larch-needles as measured by Von Hohnel and myself did not agree. Von 
Hohnel found that 100 air-dry ‘lighted’ larch-needles weighed 0-165 grm. ; 
whereas mine weighed only 0-1034, while 100 shaded leaves weighed 0-0958 
grm. Hence Von Hohnel’s larch-needles were either larger, denser, or less 
dry ; and I have calculated the transpiration according to the first possibility 
(viz. 3-4), as well as according to the surface of the larch-needles measured 
and weighed by myself (viz. 5.4). 
The existence of the larch, with its rapidly transpiring leaves, is in itself 
fatal to Miss Stopes’s hypothesis (’ 07 ) that Conifers necessarily have 
a limited rate of transpiration and ‘ xerophytic ’ foliage because the wood 
is incapable of * allowing a rapid flow of water ’. 
