Fig. 141.

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LECTURE XXXIII.

CLASS XVI.-DIADELPHIA.

THIS is the class of two brotherhoods, the stamens being united by their filaments into two sets. The flowers of this class are Papilionaceous, or butterfly-shaped; this peculiar form of their corollas is an important mark of distinction.

Two circumstances should be noted here, in order to prevent you from falling into error with respect to this class.

1st. There are some plants with filaments united in one set, but with flowers papilionaceous; these are retained in Diadelphia, though there be no apparent division in the brotherhood or set.

2d. Though the flower be papilionaceous, if it have ten separate stamens, it is placed in the 10th class; this is the case with the cassia and wild indigo.

Linnæus, in reference to the form of the flowers, arranged this tribe under a natural order Papilionacea ;-Jussieu, regarding the fruit, called the same Leguminosa.

Fig. 142 represents the sweet pea (Lathyrus odorae tus ;) at a, is the five-toothed calyx; at b, is the upper petal, called the banner; at c, are the wings, or two side petals; at d, is the keel, formed of two petals united by their edges; at c, are the ten stamens, nine united and one separate; at f, is the pistil, the base of which, in process of time, becomes the pod or legume.

The flowers of the leguminous plants are so peculiar in appearance, that they are easily recognised. They are called by botanists, irregular. The rose, pink, and bell-flower, are regular in their form; that is, there is a symmetry and equality in their parts. There may be slight inequalities in regular corollas; as in the lily we sometimes see some petals a little longer than the others; this is an exception to the general rule. It is often owing to a want of discrimination between rules and exceptions, that young persons find difficulties in

Class Diadelphia-What two circumstances to be observed with respect to this class?-Natural order Papilionacea-Leguminosa-Describe Fig. 142-Regular corollas.

understanding a science, thinking, very erroneously, that the knowledge of the one is as important as that of the other. If a clear conception of general rules be established in the mind, the exceptions will be easily learned. Irregular corollas differ so widely from the regular ones, that you will be in little danger of mistaking them for exceptions to the general rule; they constitute, indeed, a different natural family, though, according to the artificial method of classification, they may often be placed near to regular corollas. Irregular corollas are various in their forms; the papilionaceous, which we are now considering, seem, as they stand upon their stem, to consist of an upper and under part. In examining a natural flower of this kind, a pea for example, you should first observe the calyx; this is monosepalous, that is, consisting of one sepal, ending in five distinct leafy points, (see Fig. 142, a ;) the two upper ones wider than the three under ones. The peduncle is slender and flexible, (see Fig. 142, g;) thus the flower readily avoids a current of air by turning its back to the wind and rain.

In examining the corolla you will see that it is polypetalous. The first piece, or large petal, covering the others and occupying the upper part of the corolla, is called the standard or banner. This petal is evidently designed to protect the stamens and other parts of the flower from injuries by the weather. Upon taking off the banner, you will find that it is inserted by a little process or projecting part into the side-pieces, so that it cannot be easily separated by winds. The banner being taken off, the two side-pieces, or wings, are exposed to view; they are strongly inserted into the remaining part of the corolla, and their use appears to be that of protecting the sides of the flower. Upon taking off the wings, you will discover the last piece of the corolla, called, on account of its form, the keel, (carina,) or boat. This covers and protects the stamens and pistils. Upon drawing the keel downward, you will find the ten stamens, double in number to the petals; these stamens are joined together by the sides of their filaments, forming a cylinder which surrounds the pistil. One of the stamens, however, does not adhere to the rest; but as the flower fades and the fruit increases, it separates and leaves an opening at the upper side, through which the germ can extend itself by gradually opening the cylinder. In the early stage of the flower, this stamen will seem not to be separated; but by carefully moving it with a pin or needle, its filament will be found unconnected with the other nine.

The germ of the papilionaceous plant extends itself into that kind of pod called a legume. It is distinguished from the silique of the cruciform family, by having no partition in the legume. Besides, the seeds grow to one side only; but in the silique pod they are alternately attached to both edges of the partition. The legume opens lengthwise and rolls backwards; in the silique, the valves separate and diverge from the base upward. The seeds of this family have a marked scar, black spot or line, called the hilum, by which they adhere to the pod. Near this scar there is a minute opening into the body of the seed, through which moisture is imbibed at the period of its first growth or germination. The proper germ, or that part of the seed which is to be the future plant, continues to swell, and at length bursts through the coats of the seed, presenting between the divided halves, or cotyledons, the first true leaves, and the root.

Irregular corollas-In what manner should you proceed to examine a papilionaceous flower-Distinction between the legume and silique-What is said of the seeds of the leguminous tribe ?

The orders in the class Diadelphia, like those of the preceding class, are founded upon the number of stamens.

Order Pent-Octandria.

We could not expect from the character of the class, "stamens united into two sets," to find any plants with but one stamen. Those with five or eight stamens are all placed in one order called Tentoctandria, (five and eight stamens ;) here we find the Corydalis, an elegant plant with bulbous roots; the corolla is rather ringent than papilionaceous. Fumaria is nearly allied to Corydalis by natural characters. In some cases the stamens have very broad bases, and scarcely seem united in this class. We find here POLYGALA, one species of which is called Seneca snake-root; this not only produces a beautiful flower, but is valuable in medicine. many species of this genus in our woods and meadows.

Order Decandria.--Leguminous Plants.

We have

The tenth Order is wholly composed of plants with leguminous pods; the general character of these plants is, a calyx, often 5-parted, corolla 5-petalled, inserted on the calyx, and consisting of a banner, two wings and a keel; stamens generally 10, mostly united into two sets, 9 and 1; germ free; style 1; legume generally 2-valved, 1celled, sometimes transversely divided into many cells; seeds affixed to the edge on one side.

At Fig. 141, a, is a flower of this kind; b, shows the stamens divested of their petals; c, shows the pistil, the germ already exhibiting the form and appearance of the legume.

In this large family of plants with leguminous pods are many genera of great importance in the vegetable kingdom; but when we are able to give striking natural characters, there seems to be less need of particularizing each genus. The form of the corolla and the nature of the fruit, with few exceptions, settle the character of this class.

The most savage nations usually pay some attention to Diadelphous plants. When Ferdinand de Soto marched his army into Florida, before the middle of the 16th century, he found the granaries of the natives "well stored with Indian corn and certain leguminous seeds;" which were probably the Lima bean, (Dolichos,) or some species of that genus, for the natives still continue to culti

vate them.

The bean and pea tribes are found here. They consist of several different genera, as the vetch plants, Vicia, in which are many cultivated species, and the indigenous one, Americana. The Phaseolus, or kidney-bean, has its native as well as exotic species. The pea, so much valued as a table vegetable, belongs to the genus Pisum, a species of which, called Beach-pea, is found upon the shores of lakes and the sea-coast. The rattle-box (Crotolaria) with its inflated pericarp, is a favourite with children, who find it on sandy plains; it is a low pubescent plant with yellow blossoms. Of clover (Trifolium) there are many species, as the red, yellow, white, &c. The locust tribe contains many ornamental shrubs and trees.

The indigo (Indigofera tinctoria) of warmer climates, the red sandal-wood of the East Indies, the liquorice, and the sensitive plant, are all of this class. The gum-arabic is obtained from the acacia of the Nile, (Mimosa nilotica.) The liquorice of commerce is ob

Order Pent-Octandria-Corydalis-Polygala-Order Decandria-General character of plants of this order-Savages cultivate these plants-Bean and pea tribe--Indigo. liquorice, &c.

tained by boiling the roots of the Glycirrhiza, a native of Italy and France. The tamarind is a native of tropical regions. The Arabians and Africans allay their thirst by the cooling freshness of the pulp contained in its legumes. Some plants of this class seem to possess active properties; the seeds of the Lupine are said to be poisonous. A traveller states, that the banks of the Nile are often visited in the night by the hippopotamus or river-horse, a large animal which does great damage to the gardens and fields; and that the inhabitants destroy the animal by placing a quantity of the Lupine seeds near where he is expected; these he devours greedily; they soon swell in his stomach, and distend it so much as to cause death.

The Furze (ULEX Europeus) is a very common plant in Europe, though not found so far north as Sweden. It is a flower of beautiful appearance; so much so, that Linnæus, as is said, when he first beheld it, fell upon his knees, in a transport of gratitude, and thanked the Author of nature for thus beautifying the earth.

A class called Polyadelphia, or many brotherhoods, having stamens united in more than two sets, was formerly admitted, but it was thought to be unnecessary, and the genera which it contained have been transferred to the class Polyandria; the St. John's wort (Hypericum) is among the plants which were in the rejected class Polyadelphia; this has its numerous stamens in three clusters, not united by their filaments; but all the species of the Hypericum are not thus divided into separate parcels of stamens. This distinction, as the character of a class, is very properly laid aside; and the plants which were in the former 18th class, Polyadelphia, (many brotherhoods,) are now placed in the 12th class, Polyandria, (many stamens.) In the last two lectures, we have treated of two classes distinguished by the union of their filaments. In one class, Monadelphia, the general character was that of filaments united in one set, forming a tube. In this class, no particular form of the corolla was found to be general, unless we except the last order, in which the hollyhock flowers may serve as an example; having a double calyx of an unequal number of divisions, a corolla of five heart-shaped petals, united into one piece around the column formed by the united filaments.

In the class Diadelphia we found the marks of distinction to be, 1st. The union of the filaments into two sets ;

2d. The papilionaceous corolla; and,

3d. The nature of the fruits, consisting of that kind of pod called a legume, and thus forming one great natural family of Leguminous plants, which furnish many of the most delicious table vegetables; such as peas, beans, &c.

LECTURE XXXIV.

CLASS XVII.-SYNGENESIA.

We have now arrived at a class which contains a large portion of the vegetable tribes, particularly of those plants which blossom in the last summer months, and in autumn.

Furze-Class Polyadelphia, why rejected?-Recapitulation of the last two lectures -Class Syngenesia.

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b

The term Syngenesia signifies a union of anthers; this circumstance, you can readily conceive, forms a difference between this class and those which are distinguished by a union of filaments; in the one case, the tops of the stamens, or the anthers, are united, while the lower parts are separate; in the other case, the tops are separate, while the filaments, or lower parts of the stamens, are united.

The number of stamens in plants of this class is mostly 5, distinguished from the fifth class not only by the compound chaFig. 143. racter of the flowers, but by a union of anthers. In some cases, plants with five stamens have their anthers united, but having no other resemblance to those of the class Syngenesia, they are retained in the fifth class: the violet and impatiens are examples of this irregularity. This is an instance in which the artificial arrangement is made to bend to natural resemblances.

The term compound relates to the arrangement of the flowers, which are so closely connected as to have the appearance of one single flower. From the union of their stamens, these flowers are also called Syngenesious. The compound flowers have, by botanists, been distinguished under the three heads of semi-flosculous, (having ligulate florets ;) flosculous, (having tubular florets ;) and radiated, having tubular florets in the centre and ligulate at the circumference; the latter florets are called rays.

The semi-flosculous division contains a milky juice, which is bitter and of a narcotic quality; as the lettuce (Lactuca) and dandelion; their florets are all of one colour. The flosculous division usually exhibit in the leaves and roots a predominance of the bitter principle, as the burdock, (Arctium;) their florets are also of one colour. The radiated division is mostly composed of plants called Corympiferous; (from corymb and fero, to bear,) because their flowers are corymbs, as the Chrysanthemum, Aster, &c. This division includes many beautiful flowers, with splendid colours; and also affords many medicinal plants, as tansey and bone-set, (Eupatorium.) The colour of the florets in the disk and ray is often different in these flowers.

The compound flowers begin to blossom in the latter part of summer, and are found bordering upon the verge of winter. The dandelion is among the earliest flowers of spring, and one of the latest of autumn. The daisy is found in almost every spot which exhibits any marks of fertility; these are not single flowers, like the violet or rose, but crowded clusters of little florets.

The sun-flower is so large and conspicuous as doubtless to have frequently attracted your notice. If you examine one carefully, you will find it to be composed of more than a hundred little flowers, each as perfect in its kind as a lily, having a corolla, stamens, pistil, and seed. We distinguish the sun-flower into two parts,-the disk, which is the middle of the flower, and supposed to have resemblance to the middle or body of the sun; the ray is the border of the flower, or those florets which spread out from the disk, as rays of light diverge from the sun. The florets in this, as in other compound flowers,

What does Syngenesia signify ?-What are the characteristics of this class ?-How are the compound flowers divided?-Describe these divisions-Dandelion and daisy -Describe the sun-flower.