PDF - Wallace Online

vi COLOURS OF PLANTS 403Miiller to be fertilised by the humming-bird hawk moth,which flies in the morning and afternoon, when the colours ofthis flower, exposed to the nearly horizontal rays of the sun,glow with brilliancy, and when it also becomes very sweetscented.Attractive Grouping of FlowersTo the same need of conspicuousness the combination ofso many individually small flowers into heads and bunches isprobably due, producing such broad masses as those of theelder, the guelder-rose, and most of the Umbelliferae, or suchelegant bunches as those of the lilac, laburnum, horse chestnut,and wistaria. In other cases minute flowers are gatheredinto dense heads, as with Globularia, Jasione, clover, and allthe Composite and ; among the latter the outer flowers areoften developed into a ray, as in the sunflowers, the daisies,and the asters, forming a starlike compound flower, which isitself often produced in immense profusion.Why Alpine Flowers are so beautifulThe beauty of Alpine flowers is almost proverbial. Itconsists either in the increased size of the individual flowersas compared with the whole plant, in increased intensity ofcolour, or in the massing of small flowers into dense cushionsof bright colour ;and it is only in the higher Alps, above thelimit of forests and upwards towards the perpetual snow-line,that these characteristics are fully exhibited. This effort atconspicuousness under adverse circumstances may be tracedto the comparative scarcity of winged insects in the higherregions, and to the necessity for attracting them from a distance.Amid the vast slopes of debris and the huge massesof rock so prevalent in higher mountain regions, patches ofintense colour can alone make themselves visible and serve toMr. Hermanattract the wandering butterfly from the valleys.Miiller's careful observations have shown that in the higherAlps bees and most other groups of winged insects are almostwanting, while butterflies are tolerably abundant and he has;discovered that in a number of cases where a lowland flowerisadapted to be fertilised by bees, its Alpine ally has had itsstructure so modified as to be adapted for fertilisation only