where the leaves are numbered in succession, 1, 2, 3, 4, 5, 6. Commencing with the lowest leaf in these figures, and proceeding regularly through all the leaves until we reach the one directly above the first, we follow a spiral direction, make two complete turns round the stem, and pass through five leaves. This arrangment is expressed by the fraction. In figs. 100 and 101, it is shown that in

the case of alternate leaves, perpendicular lines may be drawn through the leaves placed directly over each other, and the number of these lines indicates the number of leaves in each spiral cycle, or the number of leaves between any leaf on the stem

Figs. 100 and 101.-Diagrams to illustrate the arrangement of the leaves on the stem. In each figure the cycle consists of seven leaves. In 100, the divergence between every two leaves is of a circle, or of 360°-1544. In 101, the divergence between every two leaves is of 360°-51.

and that directly above it. In both these figures it will be seen that the number of these lines is seven, and this, therefore, is the number of leaves in each cycle. But it will also be noticed that the number of turns made round the stem in completing the cycle is different. Thus in fig. 100, commencing with leaf No. 1, we reach leaf No. 8, or that directly above 1, after making three turns round the stem, and the fraction indicating this is; whereas, in fig. 101 we reach No. 8 after one turn, and the fraction, therefore, is. These fractions mark the angular divergence between any two leaves of the cycle, as represented in the divided circles at the upper part of the stems. In fig. 100, between 1 and 2 the angular divergence is obviously, while in fig. 101 it is of the circle. The object of this alternation in the position of leaves seem to be to allow them to be fully exposed to air and light, and to form wood equally all round.

105. The parts of the plants which we have now considered, the Root, Stem, and Leaves, constitute what are called the organs of nutrition or nourishment. Fluid matters are taken up by the cells of the roots from the soil, they are conveyed to the leaves, and there, under the influence of air and light, they are fitted for the purposes of plant life, and for the production of various secretions, such

as starch, gum, sugar, woody matter, gluten, oils, resins, &c. The nature of the soil has a material influence on the nourishment of the plant, and the process of manuring is conducted with the view of supplying certain substances which the plant requires for its vigorous growth, and which it cannot get from the particular soil in which it is placed. Some plants require ingredients which others do not need, and it is upon this principle that a certain rotation or change of crop is adopted.

VIII. ON THE FLOWER AND ITS VARIOUS PARTS.

106. The flower and its parts are denominated the organs of reproduction, inasmuch as they are concerned in the production of seed which contains the embryo or young plant. The parts of a flower are usually arranged in four series, or as they are called whorls:-1. The calyx. 2. The corolla. 3. The stamens. 4. The pistil. These parts are seen in figs. 102 and 103, in which S is the calyx, P the corolla, E the stamens, and STI the pistil. In fig. 102 the different series of the flower are complete, in fig. 103 the calyx and corolla are removed. These are all considered as formed by leaves altered so as to suit the particular functions which each part performs. They sometimes appear in the form of true leaves without any marked modification. The inner two of the

series are essentially connected with the production of seed, and are called essential organs (fig. 103.) The outer two are protective and nutritive organs,

When flowers

and are called floral envelopes. become double, the stamens and pistil are more or less completely changed into parts resembling the outer series, and when the alteration is complete, no seed is produced. In the eyes of a florist, the more perfect the change, the finer is the flower; while the botanist looks upon such as monstrous, and imperfect as regards the function of reproduction. 107. The parts of each series or whorl are ar

Fig. 102.-Flower of common Wallflower. S the calyx, P the corolla, E stamens.

Ped the flower-stalk,

Fig. 103. Same flower with calyx and corolla removed. E stamen, STI pistil, its upper part called the stigma, R the receptacle to which the parts of the flower are attached, GL a small gland at the base of the stamen.

ranged like leaves on the principle of alternation, and there is a remarkable symmetry as regards the number of the parts. Throughout the vegetable kingdom, the numbers which generally pre vail are 5 and 3, or multiples of them. Thus if a flower has 5 parts of the calyx, it has usually 5 of the corolla alternating with them, 5, 10, 20, &c. stamens, and 5 or some multiple of 5 in the parts of the pistil. So also with those flowers which have 3 parts in the calyx. In fig. 104 a diagram is given showing the alternation of the 5 parts of each whorl of the flower. It is also found that the numbers 2 and 4 are met with, although by no means so frequently as those already mentioned. It is worthy of notice

Fig. 104.

that flowers exhibiting 5 or 4, or multiples of these numbers in their whorls, usually belong to plants having two seed-lobes or cotyledons, and which, when they form permanent woody stems, exhibit distinct zones or circles, and have separable bark; while flowers, having 3, or a multiple of 3, in their whorls, present only one seed-lobe, and when they form permanent woody stems exhibit no distinct zones nor circles, and have no separ

Fig. 104.-Diagram to show the arrangement of the parts of the flower. There are four whorls, each consisting of five parts, which alternate with those next them.