IT is admitted by all observers that many species of flowering
plants growing on the higher alps of mountainous regions display
a more vivid and richer colour in their bloom than is displayed
in the same species growing in the valleys. That this is actually
the case, and not merely an effect produced upon the observer by
the scant foliage rendering the bloom more conspicuous, has been
shown by comparative microscopic examination of the petals of
species growing on the heights and in the valleys. Such
examination has revealed that in many cases pigment granules are
more numerous in the individuals growing at the higher altitudes.
The difference is specially marked in Myosotis sylvatica,
Campanula rotundifolia, Ranunculus sylvaticus, Galium cruciatum,
and others. It is less marked in the case of Thymus serpyllum and
Geranium sylvaticum; while in Rosa alpina and Erigeron alpinus no
difference is observable.[2]
In the following cases a difference of intensity of colour is,
according to Kerner ("Pflanzenleben," 11. 504), especially
noticeable:-- _Agrostemma githago, Campanula
[1] _Proc. Royal Dublin Society_, 1893.
[2] G. Bonnier, quoted by De Varigny, _Experimental Evolution_,
p. 55.
102
pusilla, Dianthus inodorus (silvestris), Gypsophila repens, Lotus
corniculatus, Saponaria ocymoides, Satureja hortensis, Taraxacumm
officinale, Vicia cracca, and Vicia sepium._
To my own observation this beautiful phenomenon has always
appeared most obvious and impressive. It appears to have struck
many unprofessional observers. Helmholtz offers the explanation
that the vivid colours are the result of the brighter sunlight of
the heights. It has been said, too, that they are the direct
chemical effects of a more highly ozonized atmosphere. The latter
explanation I am unable to refer to its author. The following
pages contain a suggestion on the matter, which occurred to me
while touring, along with Henry H. Dixon, in the Linthal district
of Switzerland last summer.[1]
If the bloom of these higher alpine flowers is especially
pleasing to our own æsthetic instincts, and markedly conspicuous
to us as observers, why not also especially attractive and
conspicuous to the insect whose mission it is to wander from
flower to flower over the pastures? The answer to this question
involves the hypothesis I would advance as accounting for the
bright colours of high-growing individuals. In short, I believe a
satisfactory explanation is to be found in the conditions of
insect life in the higher alps.