243 
Groom.—Remarks on the Oecology of Coniferae. 
weight of leaf. The effect of the misconception arising becomes obvious 
when we examine the results obtained by Von Hohnel in connexion with 
different specimens of one species. Von Hohnel conducted his observa¬ 
tions by means of potted plants, the pots and soil being protected from 
direct evaporation. He periodically weighed and watered the plants (and 
pots). One set of plants he kept in a well lighted position, and the other 
set in a constantly shaded position. Examining his statistics, the latter 
plants seem to be transpiring more rapidly than the plants exposed to sun¬ 
light. Von Hohnel sought to explain this as partly due to the fact that the 
shaded leaves were not exposed to rain or dew, that the structure of the 
shade-leaves is such as to promote rapid transpiration, and finally that the 
soil was moister in the shade. The first and third alleged causes were 
probably operative, and may well account for the truly greater transpiration 
per unit leaf-surface of some of the plants in the shade ; but the second 
assigned reason is not justifiable. The explanation of the apparently 
greater transpiration of the shaded leaves lies chiefly in their lighter weight: 
for I find that when judging either by absolute amount of water transpired 
by the whole plant or by the weight of transpiration per square centimetre 
of leaf-surface, the leaves exposed to the light in most cases transpired more 
rapidly. This is proved by an inspection of columns 3 and 4 (giving 
Von Hohnel’s results) and columns 5 to 8 (giving my calculations) of 
Table I. 
It is, therefore, possible that the estimate given above of Sorbus 
torminalis is too high, for I notice that it refers to a solitary shaded 
specimen. 
In Table I the estimates of the leaf-surface of the dicotylous plants are 
Von Hohnel’s; those of the Conifers are mine, and result from numerous 
measurements of the surfaces of leaves combined with Von Hohnel’s 
statistics as regards the numbers and lengths of the leaves. The following 
were my results :— 
DIMENSIONS OF CONIFEROUS LEAVES. 
In Sunlight. 
In Shade. 
Mean 
length. 
Mean perimeter or 
width of cross section. 
Alean 
Length. 
Mean perimeter or 
width of cross section. 
Pinus sylvestris 
47.3 mm. 
3-48 mm. I 
54-75 mm. 
3.32mm. ) 
> perimeter. 
? perimeter. 
Picea excelsa . 
17.18 „ 
2-88 „ ) 
16-9 „ 
2 '47 „ ) 
Abies pectinata 
12 
2 ” l 
— 
— 
> mean width. 
Larix decidua. 
27.2 „ 
0-713 „ ) 
2 3 -i » 
0-862 ,, width. 
