126 MORPHOLOGY 



fully expanded. Only in bright sunshine do they open 

 widely, while at other times they close up. White 

 and yellow are predominant colours, but these colours 

 are more intense than in Class 2. Insects with a 

 tongue of medium length are common pollinating 

 agents. The Cruciferce family of plants offers many 

 good instances of such flowers. 



4. Flowers with Completely-concealed Nec- 

 tar. — Although actinomorphic flowers predominate, 

 very many of them are irregular or zygomorphic. 

 Red, blue, and violet colours displace the white and 

 yellow of the last two classes (2 and 3). Long-tongued 

 insects are the chief pollinating agents. The honey- 

 bee, for example, may almost everywhere be found 

 sucking the honey. The advance in floral specializa- 

 tion in the flowers of this class is accompanied by a 

 distinctly higher level of specialization in the insects 

 that visit them. Several Papilionacecs, Orchidacece, 

 LabiatcB, and Scrophulariacece are illustrative examples. 



5. Social Flowers with Concealed Nectar. — 

 In these flowers the nectar is concealed, as in Class 

 4, but the flowers are associated in heads, so that 

 they are rendered very conspicuous. There is also 

 the possibility of several flowers being simultaneously 

 pollinated. The Compositce fall into this class. The 

 whites and yellows amongst them are visited by 

 insects akin to those that visit flowers with partially- 

 concealed nectar. These insects are almost always of 

 the same colour as the flowers. The reds, blues, and 

 violets, on the other hand, are visited by insects which 

 are practically the same as for flowers with concealed 

 nectar. These insects also are of the same colour. It 

 seems, therefore, that highly-organized insects prefer 

 red, blue, and violet colours, hence these colours are 

 to be regarded as a higher stage of floral coloration. 



