New Zealand Plants and their Story
The Fertilisation of the Flowers
The Fertilisation of the Flowers.
The methods by which flowers are fertilised are of high interest, and for the past half-century have received much attention. Space permits only a brief mention here.
The majority of flowering-plants have two special organs for purposes of fertilisation, the stamen and the pistil. The former produces a yellow "dust," the pollen; the latter contains within a little chamber* one or more little roundish or oval bodies, the ovules. Each ovule contains in its interior what may be called an "egg." If the pollen falls upon that part of the pistil termed the "stigma" at the right time, a union will eventually take place between some of the essential part of the pollen and the egg. This will lead to the formation of an embryonic plant within the ovule, which, when the embryo—i.e., the little plant with seed-leaves and rudimentary root and stem—is fully developed, is termed the seed.
In some instances the stamens and pistil are close together on the same flower, and pollen and stigma are ready the one for the other at the same time, in which case the flower can fertilise itself. But in a considerable number of instances self-fertilisation is impossible, and the pollen of one flower must be applied to the stigma of another. Such cross-fertilisation, as it is called, has been proved to be beneficial for many plants. A large percentage of New Zealand trees and shrubs have the pollen-bearing flower on the one plant and the ovule-bearing on another. Others again are so constructed that the pollen is ripe before the stigma of the same flower is ready to receive it, or the stigma may in other species be developed before the pollen. In all these cases cross-fertilisation is alone possible. This may take place in two ways: either the wind may carry the pollen from one flower to another, as in the genus Coprosma and in many other cases, page 39or animals may convey it dusted on some part of their bodies. In accomplishing this work, insects play a very important rôle. Birds also fertilise a few New Zealand plants, amongst others the puriri (Vitex lucens) and the waiuatua (Rhabdothamnus Solandri).
This action of insects in fertilising plants has led to a widely spread error in New Zealand, and one is frequently gravely informed that bees change the colours of flowers—"inoculating" is the term used. That is to say, the opinion is held that a bee sucking honey from, say, a white flower can turn it red, or blue, or yellow, as the case may be. Of course, neither a bee nor any other insect can do anything of the kind. If, however, the pollen of one flower is transferred by means of an insect, the wind, or any other agency, to the stigma of a closely related individual, of a different colour, the seed which is eventually produced may give rise to a plant bearing a flower coloured differently to that of the parent plant; or, in other words, a hybrid has been produced. Here, then, is the source of the error in an imperfectly understood truth.
* In the pines the ovules are not enclosed, in a chamber, and there is no stigma. The pollen is conveyed by the wind and deposited on the ovules directly.