396 



HUTCHINSON'S POPULAR BOTANY 



FIG. 486. SECTION OF PASQUE-FLOWER. 



(a) Stamens; () nectaries. 



in cells containing the blue 

 colouring principle (anthocyanin). 

 Yellow flowers, on the other hand, 

 if they change at all, keep to 

 their own series of colours 

 oranges and pure reds so that 

 there is fitness in De Candolle's 

 division of flowers into ocanthic and 

 cyanic a yellow series and a blue. 

 Here, as elsewhere in Nature, 

 the rule is not without exceptions. 

 Thus, the Yellow and Blue Scor- 

 pion-grass (Myosotis versicolor) 

 changes from yellow in the bud to 

 blue in the open corolla; and the 

 Garden Hyacinth (Hyacinthus 

 orientalis), whose generic name 

 denotes a deep purply blue colour, 

 is not infrequently pale yellow. Other exceptions might be pointed out. 

 Kerner draws attention to a third colouring principle, a scarlet-red pig- 

 ment, as yet little known ; but notably present in the blood-coloured inflated 

 calyx of the Winter Cherry (Physalis alkekengi). It may serve, he thinks, 

 to frighten animals. If this be so, the brilliant hues of flowers must 

 in some instances be looked upon as means of repulsion rather than of 



attraction. 



From Conspicuousness we come 

 to Odour. Odour and Conspicuous- 

 ness are the two means by which 

 insects are attracted to a plant from 

 a distance, just as honey-guides facili- 

 tate their search for the nectary 

 when the flower is reached. That 

 odours really do attract insects has 

 been attested by Darwin, who found 

 that they visited flowers which he 

 had covered with muslin nets. The 

 same naturalist tells us that " Nageli 

 affixed artificial flowers to branches, 

 scenting some with essential oils 

 and leaving others unscented ; and 

 insects were attracted to the former 



in an unmistakable manner. ... Of 



. 48 /. INFLORESCENCE OF PETTY n n n i_ ^ i 



SPURGE (Euphorbia pepius), a11 flowers, he further remarks, 



.showing the horned nectaries. " white is the prevailing one : and 



