Some flowers, if not fertilised by insects, have the power to fertilise themselves, and to this class belongs the sweet-pea (Plate XXXVIII.). This flower belongs to the papilionaceous (butterfly) tribe, and when a bee alights on the flower its weight presses down the underpart. While the bee is taking the nectar, the pollen bags rise and touch her on the underside of the thorax. Then she goes on to another flower whose stigma is ripe. This time the stigma rises and touches the same part of the bee’s body, and in this manner the flower is fertilised.
Plate XXXVIII
Sweet Pea
Some plants have wonderful arrangements for transferring their pollen to other flowers, some of which are so peculiar and clever that we might think they had been designed by some crafty scientist. One of these is called the salvia, and it belongs to the same family as the dead nettle. The anthers are mounted like a see-saw, and when the bee makes its way into the flower it pushes one end of the see-saw up. This causes the other end, on which the pollen bags are situated, to come down thump on to the bee’s back. The pollen is thus scattered there, and the bee also receives what may be called a pat on the back! As the salvia flower grows old its pollen bags shrivel up, but at this time the stigma is ripe. It grows longer and longer, and bends over till it is like a letter J turned upside down:
After a bee has visited some young flowers and had her back dusted with pollen, she will, without doubt, visit some of the older ones too, and it is quite easy to understand that when she enters these she rubs her back against the overhanging stigma, and the pollen adheres to it.
Another interesting plant is the violet, the nectar of which is stored at the end of the long spur, which you will have noticed. The pollen bags fit closely round the stigma, and so when pollen drops from them it does not fall out of the flower, for its passage is blocked by the tight-fitting pollen bags. When the bee comes, she has to push her tongue right up the spur, and in doing this she forces it past the pollen bags. This causes the pollen to fall out on to her head, and so it is carried to the next flower.
CHAPTER XLV
CONCLUSION
ALTHOUGH very much more could be written on this interesting subject, yet there is a limit to all things, and we come now to the end of this little book.