EFFECTS OF ENVIRONMENT ON PLANTS. 129 
of the subject may be complete in itself, we have asked Professor 
Henslow to comment upon the foregoing papers, which he does 
as follows] : — 
With reference to “ the reason of the colour changes of 
Alpine flowers ” which Mr. Cockerell suggests, if I understand 
him aright he implies that Alpine plants utilise their energies 
in making brilliantly coloured flowers at the expense of their vege- 
tative system, so that they are consequently dwarfed. According, 
however, to the investigations of JJv'lM. Bonnier and Flahault, 
colour has nothing to do with dwarfing, for plants raised by seed 
from the same individuals and grown near Paris as well as in 
high latitudes and high altitudes, have more brilliantly coloured 
flowers, and leaves of a deeper green colour in the latter situa- 
tions than those near Paris. The brilliant colour really results 
from the enhanced chlorophyllous tissues of the leaves, which 
alone makes the materials for the colours of the flowers. The 
former is a direct consequence of prolonged and less interrupted 
sunlight. The “extreme metabolism” is thus the immediate 
effect of more powerfully assimilative tissues ; therefore, so far 
as the dwarfing is concerned, it is a disadvantage. 
With reference to this last peculiarity, M. Bonnier has 
shown that when seeds of lowland plants are sown at high 
altitudes, the plants at once assume a dwarf or prostrate habit, 
internodes not being able to develop to a like extent as at 
lower altitudes ; and as a similar dwarfness uniformly occurs in 
high arctic regions as well, the cause of dwarfing is presumably 
the relatively low temperature. A corroboration of this view is 
seen in the following experiment : if plants be grown under red, 
yellow, green, blue and violet coloured glasses it will be found 
that the internodes begin to elongate in the blue-green till they 
reach a maximum under red, correspondingly with the increase 
in amount of the obscure heat rays. I think, therefore, we may 
safely attribute dwarfing in the Alps generally to low tempera- 
ture, but the brilliant colours of the flowers is undoubtedly due 
to the heightened assimilative powers of the “improved” foliage 
under sustained sunlight of high altitudes as well as latitudes. 
Mr. H. St. A. Alder supplies some interesting notes which 
quite corroborate in the main my contention ; but he will find 
from a more extended series of observations that there is no 
rule in nature without — often plenty of — exceptions. It is no 
new observation of mine that plants frequenting wet places 
are, as a rule, less hairy than others, notwithstanding Epilobium, 
hirsutum, Lythrum Salicaria and others. In all cases it is the 
majority which forms the basis of every generalisation in natural 
history, and by no means necessarily “ all,” as Mr. Alder seems 
to imply. When a generalisation can be experimentally veri- 
fied it becomes established. Thus Polygonum amphibium has 
glandular hairs when growing on land, but none when grown in 
water. 
I would venture to suggest caution in raising arguments 
