At Fig. 65, the thorn (a) remains on the stem, while the bark (b) has been peeled off. In the prickle (c) the whole ap

pears separated from the plant. The thorn appears to be an imperfectly developed bud, which has become indurated. Leaves themselves often become spines by the hardening of their midrib or primary veins, and the diminution or absence of parenchyma. Branches are sometimes arrested in their progress at an early stage of their development, and do not appear beyond the surface of the stem; they form a knot.

The thorns, in some plants, have been known to disappear by cultivation. Linnæus imagined, that in such cases the trees were divested of their natural ferocity, and became tame.

Thorns are now considered as buds, which a more favorable situation converts into luxuriant branches; they have been compared to the horns of animals.

Fig. 66.

d

d. Glands are collections of cells forming secretions. In many plants the secretions from glands give their peculiar fragrance. Glands are sometimes attached to the base of the leaf, and sometimes occur in the substance of leaves, as in the lemon and myrtle, causing them to appear dotted when held to the light. They are found on the petioles of the passionflower, and between the teeth and divisions of the leaves of many plants. Glands are composed of a single cell dilated at the apex (as Fig. 66, a); of several cells united together, the upper one being the secreting organ (b) of two secreting cells (c), or of more than two (d). The stings of the nettle are glands, formed of a single conical cell dilated at its base, and closed at the apex by a small globular button which breaks at the slightest touch, discharging an acrid fluid that enters the puncture in the skin made by the stiff, hair-like process of the gland. When a

nettle is grasped with violence the sting is crushed, and no pain is caused by the discharge of its secretion. Nettles are similar in their structure and office to the fangs of serpents. e. Scales are membraneous expansions found on the root,

stem, and branches, of plants; they are imbricated upon the calyces of many of the compound flowers, often green, but sometimes colored. We have seen in buds how important are the scales in protecting the embryo plant during the winter. Scale-like calyces surround the flowers of grasses under the name of glumes. Scales envelop and sustain the stamens and fruit of the pine, oak, chestnut, &c.

Fig. 67.

f. Tendrils (Fig. 67). A leaf-bud is sometimes developed as a slender, spiral or twisted branch. In the vine the tendrils are considered as the terminations of separate axes, or transformed terminal buds. By means of tendrils weak stems attach themselves to other bodies for support; they usually rise from the branches, in some cases from the leaf, and rarely from the leaf-stalk or flower-stalk. Tendrils are very important and characteristic appendages to many plants. In the trumpet-flower and ivy they serve for roots, planting themselves into the bark of trees, or in the walls of buildings. In the cucumber and some other plants they serve both for sustenance and shade. Many of the papilionaceous, or peablossom plants, have twining tendrils, which wind to the right, and back again. Among vegetables which have tendrils, has been discovered that property which some have called the instinctive intelligence of plants. A poetical botanist represents the tendrils of the gourd and cucumber, as "creeping away in disgust from the fatty fibers of the neighboring olive." It has been ascertained by experiments, that the tendrils of the vine, and some other plants, recede from the light, and seek opake bodies. The fact with respect to leaves is directly the reverse of this.

Some plants creep by their tendrils to a very great hight, even to the tops of the loftiest trees, and seem to cease ascending, only because they can find nothing higher to climb. One of our most beautiful climbing plants is the CLEMATIS virginiea, or virgin's bower, which has flowers of a brilliant whiteness. Its pericarps, richly fringed, are very conspicuous in autumn, hanging in festoons from the branches of trees, by the sides of brooks and rivers.

g. Pubescence includes the down, hairs, wooliness or silkiness of plants. The pubescence of plants varies in different soils, and with different modes of cultivation. The species in some genera of plants are distinguished by the direction of the hairs. The microscope is often necessary in determining with precision the existence and direction of the pubescence. It has been suggested that these appendages may be for similar pur

f. Tendrils-g. Pubescence.

poses as the fur, hair, and bristles of animals, viz., to defend the plants from cold, and injuries from other causes.

h. Bracts are rudimentary dwarfed leaves, sometimes mere scales, at others differing little from the ordinary leaf except in the smaller size. It is sometimes difficult to decide whether bracts should be ranked with the foliage, or as parts of the flower. Bracts may be situated along the peduncle or at

its base.

At Fig. 68, the real leaves are shown at b b, and the bract at a; the former being cordate and crenate, the latter lanceolate and entire.

b

Fig. 08

In some plants, as in several species of sage, the transition from leaves to bracts is so gradual, as to render it difficult to distinguish between them, and a considerable part of the foliage is composed of the bracts. In the crownimperial, the stem is terminated by a number of large and conspicuous bracts. These appendages are sometimes mistaken for the calyx. Bracts are green or colored, deciduous or persistent. The orchis tribe have green leaf-bracts. No plants of the class Tetradynamia have bracts.

LECTURE XI.

CALYX.

65. WE have considered the organs of nutrition and vegetation; these have been called the fundamental organs of plants, because they are mere modifications or transformations of them. We are now to examine more fully than we have done the reproductive organs, called organs of fructification.

a. Their names were considered when commencing the analysis of flowers; but we are now to examine them with more minute attention, and to remark upon their different uses in the vegetable economy. We have arrived at that part of the plant, which is the ornament of the vegetable kingdom. Flowers are delightful to every lover of nature; a bouquet, or even the simplest blossom, presented by a friend, interests the heart. How many pleasant thoughts are awakened by the fresh and perfumed incense which ascends from flowers! What woman does not love flowers! yet many regard them merely as beautiful objects, without being aware that they might be rendered far more interesting by a scientific knowledge of the relations and uses of their various parts. Many spend years in cultivating plants ignorant of their botanical characters, when even a few hours' study might unfold the beautiful arrangement of botanical science, and open to the mental vision a world of wonders.

Although every part of a plant offers an interesting subject for study, the beauty of the blossom seems by association to highten the pleasure of scientific research. Flowers are indeed lovely, but like youth and beauty they are fading and transient; they are, however, destined for a higher object than a short-lived admiration; for to them is assigned the important office of producing and nourishing the

h. Bracts-Difference between the real leaf and the bract.-65. Second division of vegetable organs— a. Reflections

fruit. Like them should the young improve the bloom of life, so that when youth and beauty shall fade away, their minds may exhibit that fruit which it is the business of youth to nurture and mature.

66. The Flower and its appendages.-The essential organs of reproduction in flowering plants are the Flower, the Fruit, and the Seed. The flower consists of whorled leaves or verticils placed on an axis called the thalamus or torus. There are in most perfect plants four of these whorls. It is the normal law that each of these whorls is equal in number of parts, and alternate in position.

At Fig. 69, the calyx, a a, is composed of a whorl of five equal sepals; a corolla, b b, of the five petals in an inner whorl alternating with the parts of the calyx; five stamens, cc, in a whorl within the corolla and between its parts and opposite to the pieces of the calyx; and the five parts of the pistil follow the same normal rule.

Fig. 69.

But though in many cases it is easy to trace this arrangement, there are irregularities produced by the union of one part with another by the absorption or degeneration of some portions, and by the multiplying (deduplication), or disguising of others in various Of the four whorls, the two outer are called floral envelopes; the two inner, essential organs. When calyx and corolla are both present, the plants are dichlamydeous; when one of these organs is wanting, monochlamydeous; and when both are wanting, achlamydeous. The manner in which sepals and petals are situated in the flower-bud is termed their aestivation, or præfloration, which is the same to the flower-bud as venation is to the leaf-bud. This is valvate when the sepals or petals fit by their edges, as in the petals of umbelliferous plants; imbricated when the outermost pieces cover the margins of the inner, as in the calyx of the Hypericum; twisted or contorted when each piece overtops the next one and the whole appears spirally twisted.

67. The calyx consists of verticillate leaves, called sepals or phylla. The calycine leaves are sometimes separate from each other, in which case the calyx is polysepalous, or polyphyllous; when the leaves of the calyx are united the calyx is said to be gamosepalous or gamophyllous.

a. The calyx may be wanting, as in the lily and tulip. The corolla is also wanting in many plants; as in most of the forest-trees, which to a careful observer may seem to produce no flower; but the presence of a stamen and pistil, is in botany considered as constituting a perfect flower. These two organs are essential to the perfection of the fruit; and when a flower is destitute either of stamens or pistils, it is termed imperfect. A flower is said to be incomplete when any of the seven organs of fructification are wanting. The word calyx is derived from the Greek, and literally signifies a cup; it is the outer cover of the corolla, and usually green;

66. The flower-Normal law respecting its parts-Irregularities, how caused ?-Names of the four whorls.-67. The calyx-a. Perfect or imperfect flower.

when not green, it is said to be colored. This organ is an expansion of the Lark of the flower-stalk, as appears from its color and texture. The calyx usually envelops the corolla, previous to its expansion, and afterward remains below or around its

base.

b. In the calyx are three parts, very distinct in calyces which are long and cylindric: these are, 1st, the tube, which rises from the base; 2d, the throat, above the tube; and 3d, the mouth, or the upper and expanded part; the tube of the calyx is cylindric in the pink, and prismatic in the stramonium.

c. The position of the calyx with respect to the ovary offers an important mark of distinction between different genera, and also between different natural families of plants. The calyx is said to be superior when it is situated on the summit of the ovary, as in the apple; it is inferior when situated below the ovary, as in the pink. In many plants the calyx is neither superior nor inferior, but is situated around the ovary. When the calyx drops off before the flower fully expands, it is called caducous; the petals of the poppy are, at first, inclosed in a calyx of two sepals, but these fall off before the flower is full blown. When the calyx withers, and drops off with the corolla, it is called deciduous; when it remains until the fruit is matured, it is called persistent. Upon a pea-pod the calyx may be seen as perfect as it was in the blossom. The tube of the calyx is sometimes united to the pistil, and enlarges so as to form a part of the fruit, as in the apple, pear, &c., where the dry sepals may be seen on the summit of the fruit. In the wintergreen (Gaultheria procumbens) the berries consist of the inflated, juicy sepals.

68. Perianth (from the Greek, peri, around, anthos, flower). This is the only real cup or calyx;-in the rose it is urn-form, with leaf-like divisions at the top. In the pink, the perianth is long and tubular, having the border dentate or toothed. The hollyhock has a double perianth. The term perianth is used when a flower has but one envelope, as in the tulip; it is often difficult to determine whether this envelope should be called a corolla or calyx. Involucrum (from the Latin, involvo, to wrap up); this kind of calyx is usually found at the base of an umbel, as in the carrot. It is composed of several bracts, sometimes very small, crowded into a whorl. The involucrum is said to be universal, when it belongs equally to the whole of an aggregate flower; and partial,* when it incloses one floret, which with others constitutes a compound or aggregate flower. The term involucrum is also applied to the membraneous covering in the fructification of ferns. Ament or catkint (by some classed as a mode of inflorescence) consists of many chaffy scales, ranged along a thread-like stalk or receptacle; each scale protects one or more of the stamens or pistils, the whole forming one aggregate flower. The ament is common to foresttrees, as the oak and chestnut; and is also found upon the willow and poplar. In some trees the staminate flowers are inclosed in an ament, and the pistillate in a perianth. The Spatha, or sheath, first incloses the flower, and, when this expands, bursts lengthwise and often appears at some distance below it. This is, by some botanists, considered as a petaloid bract. It

b. Parts of the calyx-c. Position with respect to the ovary -68. Perianth-Involucrum-AmentSpatha.