26 i 
Groom.—Remarks on the Oecology of Coniferae. 
(4,000), while the other dicotylous specimens had considerably smaller 
aggregate leaf-surfaces. 
2. Despite the low rate of transpiration of the single leaf or of a unit of 
its surface, at least some north-temperate Coniferae expend and need as much 
water as do ordinary dicotylous trees . 
This is evidenced by Von Hohnel’s results obtained in 1878, as these 
represent the nearest approach to a minimum (see Table I, columns 4 and 5). 
3. The need for a certain amount of water on the part of certain 
Conifers (spruce, silver firs, and some pines, &c.) is demonstrated by the 
natural distribution of these trees, the experience of foresters, and by 
the failure to grow in Continental Europe certain Conifers that thrive when 
introduced to the more humid climate of the British Isles. 
The conclusion to be drawn from these facts is that such is the aggregate 
leaf-surface of cold-temper ate Conifers that even with their xeromorphic and 
xerophytic leaves numbers of species succumb from desiccation or grow feebly 
in places where ordinary dicotylous forest trees can thrive . It is therefore 
evident that were their foliage less xeromorphic or xerophytic, the result 
would be fatal unless the assimilating surface were reduced greatly. Such 
a reduction of the transpiring surface would involve a serious reduction in 
the assimilating organs and in the capacity of the tree to maintain itself 
as such. 
As we have no comparative statistics in regard to the relative amount 
of assimilation and transpiration in different types of leaves within different 
surroundings, it is impossible to explain why the Conifer should have 
adopted the device of having a large aggregate surface with a greater 
degree of xerophytism. Yet a comparison with the oligotrophic small¬ 
leaved evergreen Ericaceae, the fact of the occurrence of various Coniferae 
on soils so poor that these species must be oligotrophic, and, finally, the 
existence of epiphytes with large leaves and xerophytic structure, cause 
one to hazard the guess that concurrent increases in the assimilatory surface 
and in the xerophytic devices generally increase assimilation in relation to 
transpiration. 
(e) The Efficiency of the Mechanism and the Survival 
of Coniferae. 
The statistics that I have given in regard to the width of the tracheae 
of the various species of Quercus might bear an interpretation different from 
the one stated above. It might be suggested that the evergreen species 
were the primitive ones, and that the evolution of the deciduous species was 
facilitated by the power of adding to the width of the tracheae. For, 
although the deciduous larch arose without any corresponding change in the 
water-conducting constituents, it is probable that increased width of the 
tracheae in more rapidly transpiring deciduous dicotylous trees is of use 
