Lobed, when leaves are deeply indented at their margins they are said to be lobed, and according to these indentures, they are said to be three lobed, four lobed, &c. Fig. 35, a, represents a three lobed leaf, as may be seen in the Hepatica triloba.

Sinuate, from the Latin sinus, à bay; this term is applied to leaves which have their margins indented with deep roundish divisions as at b, Fig. 85.

Emarginate, denotes a slighter indentation as at c, Fig. 35.

Fig. 37.

Stellated, or whorled (from stella a star), this term is applied both to leaves and flowers and relates to the manner in which they grow around the stem, as in Fig. 37.

Tubular, there are many varieties of this kind; the leaf of the onion is a complete tube; the Sarracenia or side-saddle flower has the sides of its leaf united forming a cup, which is found filled with liquid, supposed to be a secretion from the vessels of the plant. In some countries of the torrid zone is the wild pine, Tillandsia, the leaves of which are hollowed out at their base, so as to be capable of containing more than a pint. A traveller says, by making an incision into the base of this leaf and collecting the water in our hats, we could obtain a sufficient supply for the relief of the most intense thirst. The fluid is not a secretion from the plant, but is deposited during the rainy season.

Fig. 38.

b

α

The pitcher-plant (Nepenthes distillatoria) (Fig. 38), affords a most singular tubular receptacle in an appendage to its leaf; this is lanceolate; beyond the apex of the leaf a, the mid-rib extends in the form of a tendril; at the extremity of this tendril is the cylindrical cup or pitcher b, about six inches in length and one and a half in diameter; it is furnished with a lid, c. This is usually found filled with pure water, supposed to be a secretion from the plant. Insects which creep into this cup are drowned in the liquid, except a small species of shrimp which lives by feeding on the rest. The pitcher-plant is a native of Ceylon where it is called monkey cup, on account of its being frequented by these animals for the purpose of quenching their

thirst.

Compound leaves.

When several leafets grow on one petiole the whole is termed a compound leaf, as in the rose.

Pinnate, at Fig. 39, a, represents the petiole or principal leaf stalk; from this spring out other divisions, each bearing a leafet; b, b, represent the stipules or appendages, the whole taken together forms one compound pinnate leaf. The term pinnate is from the Latin pinna, a wing or pinion.

Binate; when two leafets only form the petiole, as in Fig. 39, c.

a

Fig. 40. b

second division of threes, as Fig. 40, b.

Ternate; when the leafets

a

rise from the petiole as Fig. 40, a. Biter

nate is a

Triternate is a third

Fig. 41.

Decompound, when a pinnate leaf is again divided, or has its leaves twice compound, as Fig. 41, a. At b, is a representation of thrice compound leaves.

Leaves with respect to Magnitude.

Leaves vary in size, from the small leaves of some of the

Pinnate-Binate-Ternate-Biternate-Triternate-Decompound--Size of

leaves.

forest-trees of our climate, to the spreading Palms and Bananas of the torrid zone. As we approach the torrid zone, the leaves increase in magnitude; we can however scarcely credit the reports of travellers, who say, that the Talipot tree, in the Island of Ceylon, produces leaves of such size, that twenty persons may be sheltered by one single leaf. Although this account may be exaggerated, there is no doubt of the fact, that the leaves of the torrid zone are of a wonderful size; and that whole families can make their habitations under the branches of these trees. Here we see the care of that ever kind Prov. idence, which, in countries parched the greater part of the year by a vertical sun, has formed such refreshing shelters.

Mungo Park, in his travels in Africa, remarks upon the many important uses of palm leaves; serving as coverings to cottages, as baskets for holding fruit, and umbrellas for defence against rain or sun. These leaves are a good substitute for paper, and were so used by the eastern nations. Many suppose that the scriptures of the Old Testament were originally committed to palm leaves.

The magnitude of leaves often bears no proportion to the size of the plants to which they belong. The oak, and other forest trees, bear leaves, which appear very diminutive when compared with the cabbage, or burdock.

Leaves, with respect to Duration, are,

Caducous, such as fall before the end of summer.

Deciduous, falling at the commencement of winter; this is the case with most vegetables, as far as 30° or 40° from the equator.

Persistent, or permanent, remaining on the trees amidst the changes of temperature: as the leaves of the pine and box.

Evergreen, preserving their greenness through the year; as the fir-tree and pine, and generally all cone-bearing and resinous trees; these change their leaves annually, but the young leaves appearing before the old ones decay, the plant is always green.

In our climate the leaves are mostly deciduous, returning in autumn to their original dust, and enriching the soil from which they had derived their nourishment. In the regions of the torrid zone, the leaves are mostly persistent and evergreen; they seldom fade or decay in less time than six years; but these same trees, removed to our climate, sometimes become annual plants, loosing their foliage every year. The passion-flow. er is an evergreen in a more southern climate.

Palm-leaves- Leaves not corresponding in magnitude to the size of the plant -Duration.

Leaves with respect to Colour.

Leaves have not that brilliancy of colour which is seen in the corolla or blossom; but the beauty of the corolla, like most other external beauty, has but a transient existence; while the less showy leaf remains fresh and verdant, after the flower has withered away.

The substance of leaves is so constituted as to absorb all the rays of light, except green; this colour is, of all others, best adapted to the extreme sensibility of our organs of sight. Thus, in evident accommodation to our sense of vision, the ordinary dress of nature is of the only colour upon which our eyes can for any length of time rest without pain.

But although green is almost the only colour which leaves reflect, their variety of shades is almost innumerable.

"No tree in all the grove but has its charms,
Though each its hue peculiar; paler some,
And of a wannish grey; the willow such,
And poplar, that with silver lines his leaf;
And ash far stretching his umbrageous arm:
Of deeper green the elm; and deeper still,

Lord of the woods, the long surviving oak."*

The contrast between their shades, in forests, where different families of trees are grouped together, has a fine effect, when observed at such a distance, as to give a view of the whole as forming one mass.

A small quantity of iron, united to oxygen in the vegetable substance, and acted upon by rays of light, is said to give rise to the various colours of plants. If this theory is correct, the different shades of colour in plants, must be owing to the different proportion in which the iron and oxygen are combined.

To quote the words of a celebrated Chemist, "When Nature takes her pencil, iron is the colouring she uses."

LECTURE X.

Anatomy and Physiology of Leaves.—Their use in the Vegetable System.--Appendages to Plants.

LEAVES are compared to the lungs of animals; they are organs for respiring, perspiring, and absorbing. When leaves

* Cowper.

+ This idea coincides with the supposition, that the green colour of leaves is changed to brown by the loss of an acid principle; that when the petals of flowers turn from purple to red, they have an increase of an acid. The base of this acid is oxygen.

Colour of leaves-Different shades in the colour of leaves-What is the cause of the different shades of colour in leaves ?-The use of leaves in the vegetable economy.