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by varied colors, and providing for them by secreting stores of honey; on the other hand, these insects (flies, bees, wasps, etc.), seeking the honey which satisfies their wants, at the same time carry the pollen from one flower to another, thus providing for the fertilizing of the plants. In some cases, fertilization is secured by a natural process within the organism itself; in other cases, the pollen is scattered over a region by the wind; but the most wonderful, and at the same time efficient mode of providing for the growth of vigorous plants, is fertilization by the agency of insect life.

A brief outline of the ordinary structure of the flower will introduce to a ready appreciation of the scientific interest attaching to this last mode of fertilization, both as concerning the functions of different portions of the flowers, and the relation of dependence established between higher and lower forms of organism, so that each is dependent on the other.

Every flower as it unfolds from the bud, consists of a series of whorls, or layers of substance twined or twirled round in such a manner as to unfold or coil back, as the flower opens. The outermost of these whorls {calyx) is a mere covering or sheath, usually of a green color, which protects the bud during the more tender period, curling up and withering as the flower opens, spreading forth its beauty. The second whorl {corolla) is what we more commonly regard as the flower proper, the colored leaves, or cup, or bell, according to the specific shape distinguishing the plant. The third whorl consists of a series of stalks or filaments {stamens) which as the flower matures or ripens stand up distinct from each other, each one having at its summit a little tuft or cushion {anther) covered with a fine dust or powder {pollen). The fourth or innermost whorl, the centre piece of the flower {pistil) is that in which the seed is generated and brought to maturity. We may thus say of the flower, that its outermost whorl is a temporary covering which withers and shrinks out of view, when the beauty of the inner structure is laid open; that the second is that which attracts the eye by the loveliness of its hues; while the two which belong to the internal structure of the flower are concerned with the reproduction or propagation of the plant, providing for the healthy germ from which a fresh plant of the same order may spring up. The relation of the fine yellow powder produced at the tips of the third whorl, to the seeds which are gathered together within the fourth whorl, is the matter to which special attention has been directed by the recent discoveries which have rewarded patient research. The fine powder or pollen needs to be carried to the seed, so that its properties may operate upon that seed, if it is to be fertilized, or so matured, as to fulfil its function in generating a new plant when it is committed to the soil. In many cases it is enough that the fine powder should fall down from its elevation on the seeds below. This is self-fertilization, and is easily provided for by the mere bending of the head of the flower as it approaches maturity, or by the swaying of it in the breeze. But a more difficult, and as we might be inclined to add, more precarious, because less certain, method for fertilization is required in many cases. The experiments carried on by all our gardeners, and in a still more extended scale in all our centres of botanic research, have established the fact that in many cases, the yellow powder of one plant must be in some manner carried over to the seed produced within another flower, if that seed is to yield a satisfactory result to the horticulturist.

We have thus two prominent facts here. The one is the essential importance of the pollen for fertilization; and the other, the need for the transference of the pollen from one plant to another in order to secure reproduction of vigorous growth by the sowing of the seed. As to the first, the pollen, which appears a fine powder or flour contains fluid protoplasm, that which Professor Huxley has described as the '' single physical basis of life under all the diversities of vital existence." * These pollen grains falling on the seed discharge their protoplasmic fluid upon it, and by this means contribute to fertilization. This original or primordial form of vitalising agency is carried from one part of the flower to another, and this transference is the law regulating the propagation of flowering plants.

But, just at this point, we come upon the most striking results of recent research. Though all pollen is of this primary nature, named protoplasm, it is not found to hold true that pollen is of the same value for fertilization from whatever quarter it comes.

Lay Sermons, chap, vii, p. 134.

On the contrary, most important differences result according to the source of the pollen. There is first the process of self-fertilization. But in many cases,—Mr. Darwin has shown that this holds of the majority of the orchids, —transference of the pollen from one plant to another proves to be a great advantage, if not an actual necessity for propagation of the plant. This process, known as cross-fertilization, gives a healthy and vigorous growth; want of it, will lead to degeneration, and ultimate extinction. This discovery has introduced a whole series of the most striking observations, throwing a flood of light on the distribution and interdependence of distinct forms of organism. The necessary relation between the pollen and the seed having been acknowledged, and next the value of transference of pollen from one plant to another, the first step in the line of discovery was made by the observation of a natural provision to prevent self-fertilization by rendering it impossible that the pollen of a plant should fall on the seed of that plant. This entrance on the line of discovery was made by Sprengel so far back as 1790, by whom it was observed that in many plants the pollen and the seed did

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