408. Essential unity combined with endless diversity is every where a characteristic of nature. Herein consists the perpetual charm of her presence and the perpetual reward of her diligent study. There is no better example of this happy combination than is found in the structure of the flower. Unity or uniformity, when often repeated, becomes monotony. Diversity without unity is confusion. Hence, in our study of the thousand forms in which God has attired the flower we shall arrive at no satisfactory result until we come to discern that unity of plan, that simple idea of the flower in which' all its diversities harmonize. There is such an idea. It originated in the Infinite Mind. Let us search for it

409. The floral organs. Wo have already seen that the flower may consist of four sets of organs - calyx, corolla, androecium, gynoecium; or of four kinds of organs - sepals, petals, stamens, pistils, each arranged circularly around a common center.

410. Symmetry of the flower. Now as the leaves of a branch are definitely apportioned into equal cycles, we naturally look for a corresponding symmetry in the flower. Each set of organs should consist of at least one cycle. And as the cycle itself may vary numerically, being 2-leaved, 3-leaved, 5-leaved, etc., in different species, so in the flower each cycle or set may bo 2-parted, 3-parted, 5-parted, eta That is, the sepals, petals, stamens, pistils, may each, bo two in number, or three, or four, or five in number, etc.

411. Again, in relative position the organs of each set, as a rule, alternate with the organs of each adjacent set; the petals alternate with the sepals and stamens, the stamens with the petals and pistils. This alternation accords with the opposite and verticillate arrangement of leaves, where (§ 226) the leaves of any given circle do not stand exactly over the leaves of the next circle below, but over the intervals between them. In a word,

412. The typical flower, one that exemplifies the full idea of the floral structure, consists of four different circles of organs, each circle having the same number of separate, alternating parts. Such a flower is not only

Perfect, having both the essential organs, but also

Complete, having the four kinds of organs.

Regular, the organs of the same kind similar, and Symmetrical, the same number of organs in each whorl.

413. Seldom realized. Happily, this our conception of the typical flower is not often realized in nature, although the tendency toward it is universal. Deviations occur in every imaginable mode and degree, causing that endless variety in the floral world which we never cease to admire.

414. Examples. In our cut (Pink, 258) illustrating the organization of the flower the tendency in this direction is evident, but the stamens are too many and the pistils seem too few. Among the Flaxworts and the Houseleek tribe, however, are some good examples. The flower of the flax combines very nearly all the conditions above specified. It is complete, regular, symmetrical Its organs are alternate and all separate, and (disregarding the slight cohesion of the pistils at their base) this flower well realizes our type. But

260, bi8, Flower of Crassula lactea, regular, symmetrica], organs distinct 261, Diagram showing its plan

260, bi8, Flower of Crassula lactea, regular, symmetrica], organs distinct 261, Diagram showing its plan. 262, Flower of the Scarlet Flax. 263, Diagram of its plan.

415. The flowers of Crassula, an African genus sometimes cultivated, afford unexceptionable examples, the sepals, petals, stamens, and pistils each being five in number, regularly alternating and perfectly separate.

416. Flowers of sedum. Admitting two whorls of stamens instead of one, we have a good example of our type in stone-crop (Sedum ternatum), a little fleshy herb of our woods. Its flowers are both 4-parted and 5-parted in the same plant. See also the 12-parted flowers of the common honseleek.

417. How to study the flower If, with this type as our adopted standard of the floral structure, we compare any of the myriads of different forms which occur, we shall be able to trace out the features of the general plan even among the widest deviations. The more important of them are included in the following synopsis:-

1. Variations in the radical number of the flower.

2. Deficiencies rendering the flower a, Incomplete, 6, Imperfect, c, Unsymmetrical, dt Organs opposite.

3. Redundancies, a, In the multiplication of organs, b, In appendicular organs.

4. Union of parts.

a, By cohesions, 6, By adhesions.

5. Irregularities of development, a, In homogeneous parts, b, In the receptacle.

6. Combined deviations.

We shall consider these several topics in their order.

418. The radical number of the flower is that which enumerates the parts composing each whorl. It varies from one to twenty, and is expressed thus: V, 3V, 4V, 5V, etc. which mathematical expressions are to be read by the words, dimerous (δiς, two, έρος, part), or 2-parted; trimerous, or 3-parted; 4-merous, or 4-parted; pentamerous, or 5-parted; 6-merous, or 6-parted, eta

419. Exogens and endogens distinguished. Pentamerous (5V) flowers, like the rose, flax, when each whorl is (naturally) 5-parted, are more generally characteristic of the exogenous plants, 3V flowers of the endogens, as the lily, Trillium. The flowers of Fuchsia are 4V, of Circaea V, and of Hippuris 1 V.

420. Deficiencies. Incomplete flowers often occur. They lack some one or more entire sets of organs. When only one of the floral envelops, the calyx, exists, the flower is said to be apetalous or monochlamydeous (xλavς, a cloak), as in elm, Phytolacca. These terms are also loosely applied to such plants as rhubarb, Anemone, liverwort, where the pieces of the perianth are all similar, although in two or three whorls. When the perianth is wholly wanting, the flower is said to be achlamydeous or naked, as in lizard-tail (264.)