COLOURS OF FLOWERS AS A MEANS OF ATTRACTING ANIMALS. 187 



same head does not always consist only in the enlargement of one side, but in 

 many plants in the actual development of different forms of flower. In these 

 the flowers of the centre stand erect and are tubular, while those of the 

 periphery' radiate outwards, are larger, coloured much more brilliantly, and are 

 shaped either as short broad plates as in the Milfoil (Achillea), or like long 

 narrow tongues as in Arnica montana. In the Cornflower [Centaurea Cyanus, 

 cf. fig. 252^3) and in allied species the peripheral flowers assume the form of 

 funnels with split edges. One seeks in vain for anthers and stigmas inside these 

 flowers; they have become unfruitful and sterile, and in this way a complete 

 division of function has taken place in the two kinds of flowers of the Corn- 

 flower capitulum. Here it is only the flowers of the centre which are provided 

 with stamens and pistils, and which conceal honey at the base of their small 

 tubes; these alone are fertile. On the other hand, they are insignificant in 

 appearance, and at a little distance would not be noticed. Thus the sterile, 

 funnel-shaped flowers, visible from a distance on account of their beautiful azure 

 blue, surround their fruitful neighbours, and perform the task of attracting the 

 insects to them. This remarkable division of labour in flowers of one and the 

 same capitulum seen in Cornflowers may be also noticed in many cymose 

 inflorescences — as, for example, in the Guelder-rose (Viburnum Opulus) and in 

 Hortensias (Hyclrangcea Japonica, quercifolia, &c.; cf. fig. 222^). Of course 

 only in the wild specimens, for the Guelder-rose grown in gardens, as well as 

 those plants which horticulturists call Hortensias, have inflorescences consisting 

 entirely of sterile flowers from which no fruit can be produced. 



While in the last-mentioned plants the stei'ile flowers which attract insects 

 are found at the circumference of the capitulum or umbel, one meets with a 

 bunch of sterile flowers at the top of the racemose inflorescence in many species 

 of Museari, allied to the Hyacinths (e.g. Muscari comosum and tenuifolium; 

 cf. fig. 252^). These are very remarkable on account of their bright colour, and 

 obviously perform the same function on behalf of the less conspicuous fruitful 

 flowers below as do the sterile flowers in the capitulum of the Cornflower. 



When the bracts enveloping the flower heads assume the function of alluring 

 insects, and are consequently coloured white, yellow, red or blue, each of these 

 structures singly is usually of such a small size that it could not be seen even at 

 a very little distance; but their aggregate efiect is such that the whole inflorescence 

 is conspicuous from afar. The dry scales surrounding the flower-heads are coloured 

 snow-white, golden-yellow, or rose-red in the species of Heliehrysum known as 

 Immortelles — for example, in the sacred flower which the Greek pilgi-ims bring 

 with them from Mount Athos (Heliehrysum virgineum), in the beautiful 

 Eelichrysiim frigidum of the Corsican uplands, in the yellow-headed Heliehrysum 

 arenarium growing on the sandy heaths of the Rhine valley, and in the numerous 

 species spread over the rocky heights in tJie Cape. It is evident that the effect of 

 the scaly, coloured envelopes is materially increased when the flower-heads they 

 surround are massed together in numbers forming dense tufts. It thus happens 



