CHAPTER XXII.

FLOWER STRUCTURES IN RELATION TO INSECTS

The relation between flowers and insects is one of mutual help and advantage, and therefore is quite different from that in the cases where the animals eat the plants or vice versa.

When we examined flowers in general, we found that the insects do a very important work in carrying the pollen from flower to flower, and that their structures are arranged to attract insects and to make it easy for them to get covered with the pollen of one flower and leave it on the next. If we look at the details in some of the flowers, we shall see how elaborate their structures may be, and how carefully they are planned to make sure that the bee gets the pollen on its body and carries it with it to the neighbouring flowers.

In the simple circular flowers, such as roses, poppies, and lilies, the bee can enter freely from any side that it chooses, and it generally goes straight to the centre. Many of these simple flowers, therefore, have large numbers of stamens which stand up in a crown in the middle, so that the bee must touch and stir some of them as he dives in the centre for the honey.

In others which are nearly circular, there is a little difference between the back and front of the flower, and the stamens are so placed that the visiting insect must touch them. For example, look into the bell of a foxglove, where you will find only four stamens, but they are bent so that the anthers together form a kind of platform in the front of the flower, over which the bees must pass as they enter (~see~ fig. 117). Frequently the stamens bend in this way towards the front of the flower, and in many cases the whole flower becomes quite definitely two-sided, with a front and back, and a special place for the entrance of the bee. This is the case with the violet, pea, monkshood, and many others (~see~ fig. 118).

When flowers have this form, you frequently find that the number of stamens is quite small, seldom more than ten, and often less.

A plant of this kind very interesting to watch is the yellow gorse. If you can get up and sit by a flowering bush from about half-past five to seven one sunny morning, you will be able to learn a great deal about the doings of the bees and flowers.

First examine a flower so that you know how it is arranged. At the back lies the big petal, or “standard,” as in the pea; there are two side wings, and in the front the two petals close together forming the “keel.” The two-sidedness of this flower is very well marked. Inside the keel you will find ten stamens, all joined to form a tube except the back one, which is free, and inside them lies the carpel with its curved style. When the stamens are ripe they are so fitted that they lie inside the keel of the petals in a bent form, and when they are pressed from above they fly out with a little explosion and scatter the pollen dust about. Now watch a bee alighting on the flowers; he presses the two front petals with his legs to open them to get at the honey, and the stamen explosion covers him all over with pollen. Then he goes to the other flowers, but perhaps the next one he visits has already exploded and the ripe stigma is exposed in the front of the flower, and as he settles he touches it with his furry body all covered with pollen, and leaves some on it. If you watch the bees doing this yourself, you will find out a number of things which I have not told you, while you may notice how some of the bees are lazy and enter the wrong side of the flower, others are stupid and go to flowers which have already been visited several times, and therefore are of no use, while other bees which come late may open up buds which were not ready for them and steal the honey before the stamens are ripe enough to smother them with pollen. I have watched them opening buds which were still so tightly closed that it took them all their strength to get in. But we must not stop too long with one flower, for almost every flower has some special arrangement of its own, and all are worth study.

The primroses and cowslips are interesting, as they have two kinds of flowers. It you gather a bunch of primroses and look into them you will find that in some you can see the little central green ball of the stigma, and in others at the top of the tube are the five small anthers. These two kinds of flowers make an arrangement which ensures that the pollen from the one kind of flower reaches the stigma of the other. A big fly like the wasp-fly, and several others, visit these flowers most frequently, and carry the pollen from flower A (~see~ fig. 120) to the stigma of B, and the pollen of B to the stigma of A.

As we noticed before, the chief duty of the petals is to act as flags to attract the visiting insects by their bright colours. Now we find that some flowers club together, and grow clustering closely on one head, so that it is sufficient for a few of them to have the flag petals which attract the insect to the group, as it goes from one to the other when once it is there. When a few of the flowers do this, the rest can economise in petals and have quite small ones, and yet all the same they have a good chance of insect visits. Such an arrangement as this is found in the daisy (~see~ fig. 121). A single daisy is not one flower, but a whole bunch of flowers, in which some of the outer flowers of the bunch (~see~ fig. 121 (~b~)) form big petals, while all the inner ones (fig. 121 (~c~)) are quite small and inconspicuous, and by themselves would hardly attract any visitors. Just the same thing happens in the cornflower, sunflower, and very many members of the daisy family. The big outer petals attract the insect, and once on the head of flowers it walks about over them, and they all get the benefit.

In such cases we get ~a division of labour among the flowers of a head~, and this represents what is perhaps the highest state of development that flowers have reached.