WHILST it is true that plants cannot speak or walk about, yet they live a separate life of their own. They breathe and sleep, feed and digest just as animals do, but in a different manner. In order that we may understand more about this and the use that bees are to them, we must first learn a little about the construction of the flowers themselves. Let us choose a daffodil about which to speak, for it is both interesting and easily obtainable.
You will know that it is made up of “flower leaves,” and that there is no calyx like that of a primrose, for instance. The corolla is a deep yellow tube, and to it the flower leaves are joined. If now we cut the flower in half, we find that there is a long rod, called the style, at the end of which is a kind of sticky knob, called the stigma; this you will see on Plate XXXVI. There are six smaller rods grouped round the style, and these are called the stamens. They are thickened at the end near the stigma, and the thickenings are called the anthers. The anthers are the pollen-bearing parts of the flower, and though their position often varies, you will find both anthers and stigma in nearly every kind of flower. Below the corolla of the daffodil is the ovary, and this is where the seeds are formed. If we look in the ovary of our daffodil, we shall see several tiny round objects of a transparent nature. These are called the ovules, and in time they may become seeds. There is a remarkable difference between an ovule and a seed, for if we planted one of the former, it would simply wither and decay in the ground. If, however, we set a seed, sooner or later a plant, like that from which the seed was taken, will spring up.
An ovule only becomes a seed after it has been fertilised, and this is accomplished by some pollen being placed on the stigma. The style is a kind of tube, and is connected with the ovary, and when grains of pollen fall on the stigma they send out long shoots, called pollen tubes. These pollen tubes grow down the style till they reach the ovary. Each pollen tube then finds an ovule, forces its way in, and pours in nutrition from the pollen grain on the stigma above. The ovules then undergo certain important changes, and are turned into seeds. Pollen grains are of all sizes and shapes, but they are generally very tiny indeed. When I tell you that hundreds of grains of the kind would take up no more room than a pin-head, you will understand how very minute and wonderful are these tiny pollen tubes.
The change in the ovules, which we have just read about, is called fertilisation, and we know that this is necessary to a plant if its ovules are to be changed into seeds. We might imagine that there is no difficulty about this in the cases of flowers where there are both anthers and stigma, but it is a law of Nature that it is not desirable for flowers to be fertilised by their own pollen. Why this should be we do not know, but it certainly is an actual fact. By this I do not mean to say that flowers cannot be fertilised by their own pollen, but that they produce healthier and more numerous seeds when fertilised by pollen from another plant. Pollen from another flower of the same plant will not do, but it should be from another plant altogether. Of course the two plants must be of the same kind, for it would not do to expect the pollen of a sweet-pea to fertilise a wallflower.
Some flowers will not be fertilised at all by pollen from their own plant, and one of these is clover. Mr. Darwin, a scientist who has taught us a great deal about this subject, tried an experiment in which he fertilised twenty heads of clover by the pollen of other clover plants. They produced no less than 2290 seeds, but when another twenty heads of clover were kept from being fertilised by any but their own pollen, not a single seed was produced.
No doubt you will be wondering why a flower is not fertilised when anthers covered with pollen surround the stigma. The explanation is very simple, for the stigma has to become ripe before it can receive any pollen. In some plants the stigma is ripe before the anthers give off pollen, whilst in others all the pollen is given from off the anthers before the stigma becomes ripe. Thus we see how Nature prevents a flower from fertilising itself.