VI 
COLOURS OF PLANTS 
403 
Muller to be fertilised by tbe humming-bird hawk moth, 
which flies in the morning and afternoon, when the colours of 
this flower, exposed to the nearly horizontal rays of the sun, 
glow with brilliancy, and when it also becomes very sweet- 
scented. 
Attractive Grouping of Flowers 
To the same need of conspicuousness the combination of 
so many individually small flowers into heads and bunches is 
probably due, producing such broad masses as those of the 
elder, the guelder-rose, and most of the Umbelliferae, or such 
elegant bunches as those of the lilac, laburnum, horse chest- 
nut, and wistaria. In other cases minute flowers are gathered 
into dense heads, as with Globularia, Jasione, clover, and all 
the Compositse • and among the latter the outer flowers are 
often developed into a ray, as in the sunflowers, the daisies, 
and the asters, forming a starlike compound flower, which is 
itself often produced in immense profusion. 
Why Alpine Flowers are so beautiful 
The beauty of Alpine flowers is almost proverbial. It 
consists either in the increased size of the individual flowers 
as compared with the whole plant, in increased intensity of 
colour, or in the massing of small flowers into dense cushions 
of bright colour ; and it is only in the higher Alps, above the 
limit of forests and upwards towards the perpetual snow-line, 
that these characteristics are fully exhibited. This effort at 
conspicuousness under adverse circumstances may be traced 
to the comparative scarcity of winged insects in the higher 
regions, and to the necessity for attracting them from a dis- 
tance. Amid the vast slopes of debris and the huge masses 
of rock so prevalent in higher mountain regions, patches of 
intense colour can alone make themselves visible and serve to 
attract the wandering butterfly from the valleys. Mr. Herman 
Muller’s careful observations have shown that in the higher 
Alps bees and most other groups of winged insects are almost 
wanting, while butterflies are tolerably abundant ; and he has 
discovered that in a number of cases where a lowland flower 
is adapted to be fertilised by bees, its Alpine ally has had its 
structure so modified as to be adapted for fertilisation only 
