POLYPETAL^— RANUNCULACE^. 121 



flower. This arrangement favours cross - pollination. The 

 insect, when visiting the inflorescence, commences at the 

 lowest flowers, and travels up the inflorescence. In this manner 

 pollination by the pollen even of the same plant is averted. 

 The long-stalked nectaries are completely concealed from out- 

 side view, nor can their honey be reached excepting with great 

 difficulty by any insects other than humble-bees. The Monks- 

 hood-flower is a flower especially adapted for pollination by the 

 agency of these particular insects, consequently it is absent from 

 those regions of the earth which are without humble-bees. 



Comparison between the pollination and flowers of the Butter- 

 cup and of the Monkshood. — The yellow Buttercup - flower 

 is actinomorphic, and is directed upwards. Inasmuch as its 

 nectaries are feebly concealed and easily accessible, insects 

 with quite short tongues can discover and reach the honey. 

 The flower is therefore visited by many (more than sixty) kinds 

 of insects. These alight on the petals or on the carpels, and 

 may cause cross-pollination or self-pollination. The blue Monks- 

 hood -flower is zygomorphic, and is inclined to the horizon. 

 Its honey is carefully concealed and protected, so that only 

 specialised insects can discover and reach it. The flower is 

 pollinated exclusively by one group of insects — humble-bees — 

 which visit in one particular way, and necessarily effect cross- 

 pollination as they go from plant to plant. Self-pollination is 

 impossible in the Monkshood-flower. The Monkshood- and 

 Buttercup-flowers thus illustrate the fact that the colours and 

 shapes of flowers are associated with the varieties of insects 

 which visit and pollinate those flowers. We also see that the 

 irregular zygomorphy is a means employed to cause the visiting 

 insect to deal with the flower in a particular manner so as to 

 ensure cross-pollination. Finally, we note that the zygomorphic 

 flowers are associated with certain classes of insects, not, as is 

 the Buttercup, with many varieties of flower-visiting insects. 



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