Lecture X  Bees And Flowers   Continued…

But we are not yet nearly at an end of the contrivances of flowers to secure the visits of insects. Have you not observed that different flowers open and close at different times? The daisy receives its name day’s eye, because it opens at sunrise and closes at sunset, while the evening primrose (Aenothera biennis) and the night campion (Silene noctiflora) spread out their flowers just as the daisy is going to bed.

What do you think is the reason of this? If you go near a bed of evening primroses just when the sun is setting, you will soon be able to guess, for they will then give out such a sweet scent that you will not doubt for a moment that they are calling the evening moths to come and visit them. The daisy opens by day, because it is visited by day insects, but those particular moths which can carry the pollen-dust of the evening primrose, fly only by night, and if this flower opened by day other insects might steal its honey, while they would not be the right size or shape to touch its pollen-bags and carry the dust.

It is the same if you pass by a honeysuckle in the evening; you will be surprised how much stronger its scent is than in the day- time. This is because the sphinx hawk-moth is the favourite visitor of that flower, and comes at nightfall, guided by the strong scent, to suck out the honey with its long proboscis, and carry the pollen-dust.

Again, some flowers close whenever rain is coming. The pimpernel (Anagallis arvensis) is one of these, hence its name of the “Shepherd’s Weather-glass.” This little flower closes, no doubt, to prevent its pollen-dust being washed away, for it has no honey; while other flowers do it to protect the drop of honey at the bottom of their corolla. Look at the daisies for example when a storm is coming on; as the sky grows dark and heavy, you will see them shrink up and close till the sun shines again. They do this because in each of the little yellow florets in the centre of the flower there is a drop of honey which would be quite spoiled if it were washed by the rain.

And now you will see why cup-shaped flowers so often droop their heads – think of the harebell, the snowdrop, the lily-of-the- valley, the campanula, and a host of others; how pretty they look with their bells hanging so modestly from the slender stalk! They are bending down to protect the honey-glands within them, for if the cup became full of rain or dew the honey would be useless, and the insects would cease to visit them.

But it is not only necessary that the flowers should keep their honey for the insects, they also have to take care and keep it for the right kind of insect. Ants are in many cases great enemies to them, for they like honey as much as bees and butterflies do, yet you will easily see that they are so small that if they creep into a flower they pass the anthers without rubbing against them, and so take the honey without doing any good to the plant. Therefore we find numberless contrivances for keeping the ants and other creeping insects away. Look for example at the hairy stalk of the primrose flower; those little hairs are like a forest to a tiny ant, and they protect the flower from his visits. The Spanish catchfly (Silene otites), on the other hand, has a smooth, but very gummy stem, and on this the insects stick, if they try to climb. Slugs and snails too will often attack and bite flowers, unless they are kept away by thorns and bristles, such as we find on the teazel and the burdock. And so we are gradually learning that everything which a plant does has its meaning, if we can only find it out, and that even very insignificant hair has its own proper use, and when we are once aware of this a flower-garden may become quite a new world to us if we open our eyes to all that is going on in it.

But as we cannot wander among many plants to-day, let us take a few which the bees visit, and see how they contrive not to give up their honey without getting help in return. We will start with the blue wood-geranium, because from it we first began to learn the use of insects to flowers.

More than a hundred years ago a young German botanist, Christian Conrad Sprengel, noticed some soft hairs growing in the centre of this flower, just round the stamens, and he was so sure that every part of a plant is useful, that he set himself to find out what these hairs meant. He soon discovered that they protected some small honey-bags at the base of the stamens, and kept the rain from washing the honey away, just as our eyebrows prevent the perspiration on our faces from running into our eyes. This led him to notice that plants take great care to keep their honey for insects, and by degrees he proved that they did this in order to tempt the insects to visit them and carry off their pollen.

The first thing to notice in this little geranium flower is that the purple lines which ornament it all point directly to the place where the honey lies at the bottom of the stamens, and actually serve to lead the bee to the honey; and this is true of the veins and marking of nearly all flowers except of those which open by night, and in these they would be useless, for the insects would not see them.

When the geranium first opens, all its ten stamens are lying flat on the corolla or coloured crown, as in the left-hand flower in Fig. 58, and then the bee cannot get at the honey. But in a short time five stamens begin to raise themselves and cling round the stigma or knob at the top of the seed-vessel, as in the middle flower. Now you would think they would leave their dust there. But no! the stigma is closed up so tight that the dust cannot get on to the sticky part. Now, however, the bee can get at the honey-glands on the outside of the raised stamens; and as he sucks it, his back touches the anthers or dust-bags, and he carries off the pollen. Then, as soon as all their dust is gone, these five stamens fall down, and the other five spring up. Still, however, the stigma remains closed, and the pollen of these stamens, too, may be carried away to another flower. At last these five also fall down, and then, and not till then, the stigma opens and lays out its five sticky points, as you may see in the right-hand flower, Fig. 58.

But its own pollen is all gone, how then will it get any? It will get it from some bee who has just taken it from another and younger flower; and thus you see the blossom is prevented from using its own pollen, and made to use that of another blossom, so that its seeds may grow healthy and strong.

The garden nasturtium, into whose blossom we saw the humble-bee poling his head, takes still more care of its pollen-dust. It hides its honey down at the end of its long spur, and only sends out one stamen at a time instead of five like the geranium; and then, when all the stamens have had their turn, the sticky knob comes out last for pollen from another flower.

All this you may see for yourselves if you find geraniums* in the hedges, and nasturtiums in you garden. But even if you have not these, you may learn the history of another flower quite as curious, and which you can find in any field or lane even near London. The common dead-nettle (Fig. 59) takes a great deal of trouble in order that the bee may carry off its pollen. When you have found one of these plants, take a flower from the ring all round the stalk and tear it gently open, so that you can see down its throat. There, just at the very bottom, you will find a thick fringe of hairs, and you will guess at once that these are to protect a drop of honey below. Little insects which would creep into the flower and rob it of its honey

without touching the anthers of the stamens cannot get past these hairs, and so the drop is kept till the bee comes to fetch it. (*The scarlet and other bright geraniums of our flower-gardens are not true geraniums, but pelargoniums. You may, however, watch all these peculiarities in them if you cannot procure the true wild geranium.)

Go to Lecture 10-Part 3 here.