Xerophily and the Deciduous Habit. 
185 
Hence I do not regard the undoubted xerophily of the 
Coniferales as out of place at the present time, or out of touch 
with modern requirements. On the contrary, 1 regard the primitive 
and general xerophily of the Gymnosperms, transmitted to the 
modern conifers, as an important factor which enables the latter 
plants to hold their own in the deciduous forests of the north 
temperate zone, and as being necessary for the continuance of the 
conifers in a region, which, for more than half the year, is eco¬ 
logically xerophytic. 
With regard to Miss Stopes’s general conclusion, that the 
xerophily of the Coniferales is phylogenetic and not adaptive, it 
appears to me that the acicular leaf of many northern species of 
conifers, and the deciduous habit of a few others, furnish important 
exceptions to the truth of the dictum. It is usually admitted that 
the broad-leaved conifers are more primitive than their needle¬ 
leaved relatives; and it will not be denied that the deciduous 
species of conifers are more recent than the evergreen members of 
that order. I see no difficulty in regarding both the acicular leaf 
and the deciduous habit of certain conifers as due to environmental 
factors. These two forms of xerophily, instead of being out of 
place at the present time, may be regarded as factors which account 
for the present wide and general distribution of northern conifers; 
and, instead of needing to be explained away, they are precisely the 
factors which furnish a partial, if not indeed an adequate and a 
sufficient explanation of the frequent dominance and successful 
competition of northern conifers among phylogenetically higher 
forms. 
There is a further question into which I have not entered, 
namely, what is xerophily ? It appears to me that no satisfactory 
answer to this question has yet been given by any botanist. It is 
not sufficient to quote figures relating to the amount of water lost 
during transpiration. At best, such figures are only comparative, 
and there is no accepted standard of comparison. Before a solution 
of this problem is found, a great deal of research is necessary, not 
only along conventional lines, but also by methods which, at present, 
are foreign to the laboratories of the schools. 
Manchester, 
May 29th, 1907. 
C. E. MOSS. 
