Milkweed, the popular name for plants of the genus Asclepias (named in honor of Aescu-lapius), which includes about 40 species, half of which are North American and the remainder natives of Central and South America. They are all herbaceous plants, with thick deep roots, and mostly with a copious milky juice, bearing their flowers in simple umbels. Few plants present flowers in which the ordinary floral structure is so obscure, and it is not easy to explain them without numerous elaborate diagrams; in general terms it may bo said that the parts of the flower are in fives; the five-parted calyx is persistent; the deeply five-parted corolla is reflexed; immediately within the corolla is a curious structure called the crown, made up of appendages to the stamens, which are themselves united into a tube by their filaments; behind each anther is borne a curious erect hood-like appendage, from which projects a small horn; these appendages are petal-like, and together form a conspicuous portion of the flower; the anthers closely surround and partially adhere to the broad stigma; each anther cell contains a pear-shaped, waxy mass of pollen, and two adjacent masses from two contiguous anthers are suspended by a stalk from a blackish adhesive gland which is borne on the margin of the broad stigma; these pollen masses, by means of the adhesive glands, stick to insects which visit the flowers for honey, and are thus dislodged and borne to other flowers; bees are frequently quite disabled by these pollen masses, which adhere to their legs in such numbers as to prevent them from climbing upon their combs, and they fall down and perish.
The ovaries are two, ripening into two large follicles, which open and expose the flattened seeds imbricated over a large placenta, each furnished with a tuft of long, beautiful silky hairs, by the aid of which it may be wafted to a distance by the wind; on account of these silky hairs the plant is frequently called silkweed. The flowers in most species are showy and fragrant, and some are cultivated as ornamental plants; the young shoots of our common species are valued by many as a substitute for asparagus; the bark of their stems is very tenacious, and various partially successful attempts have been made to obtain from them a textile fibre and a paper stock; the plants are not abundant enough in the wild state to afford any considerable supply, and no experiments have been made to ascertain whether their cultivation as a fibre-producing plant would be profitable. The beauty of the silky down of the seeds early attracted attention, and many attempts have been made to utilize it; but the hairs are very weak and brittle, and without the roughness or angularity which makes it possible to spin other fibres; when mixed with cotton it has been spun and woven into fabrics which have a silky lustre and take brilliant dyes, but the manufacture has not been prosecuted; the principal use made of the down is in the stuffing of pillows. - The common milkweed (A. Cornuti) is the most abundant species, and is to be found in rich grounds almost everywhere; although it is a native of America, Linna3us called it A. Syriaca, a name which has been properly superseded; in the southern states it is known as Virginia swallow wort and Virginian silk.
The purple milkweed (A. purpurascens) is a dark-tlowered species; A. variegata has nearly white flowers; A. incarnata, with fine rose-purple flowers, is very common in wet grounds, and is known as the swamp milkweed; the blunt-leaved milkweed (A. oltusifolia) is a common species, readily recognized by its clasping, sessile leaves, and its single umbel of large but dull-colored flowers; the four-leaved milkweed, the most delicate of the genus, blooms in woods in June, and is well marked by having one or two whorls of four leaves; A. rerticillata, very common on dry hills, has whorled leaves, which are so narrow as to give the plant a very different aspect from other species. The most showy of all our native milkweeds is A. tuberosci, more generally called butterfly weed and pleurisy root; it is quite common, especially southward; the root is large, fleshy, and white; the stems are more or less decumbent and roughly hairy, very leafy, and branching at the summit, where it bears numerous umbels of bright orange-colored flowers, which are exceedingly showy and allow the plant to he distinguished at a great distance; in this species the juice is scarcely milky.
As one of its popular names indicates, the plant is used in medicine, the root being the officinal portion; its action is diaphoretic and expectorant without being stimulant, and in large doses is purgative. This plant is much valued abroad as an ornamental one, and its roots are a part of the regular stock of the growers of bulbs and tubers; in this country it is seldom seen in gardens, but there is no flower of its color capable of producing a more brilliant effect. Several of our common species are valued in European gardens, as is A. Douglasii, a conspicuous plant from California, with large leaves, very white with woolly hairs, and large lilac-purple fragrant flowers. A. Curassavica, from South America, naturalized in Florida, with flowers of orange scarlet, is a common greenhouse plant, and is frequently set out in the border for summer blooming; this has emetic properties, and is used in the West Indies under the incorrect name of ipecacuanha. Active properties pervade the genus, and several of the species have a reputation among the herb doctors. - The genus is the typical one of the Asclepiadacece, which includes more than 130 genera and over 1,000 species.
Of the other native genera, the green milkweeds, of the genus acerates, differ from the true milkweeds in the absence of a horn to the stamineal hood. A twining plant, vince-toxicum nigrum, with very dark purple flowers, has escaped from cultivation in some places, as has the Grecian silk, periploca Graeca, which is often seen in gardens as an ornamental climber. From Pennsylvania southward are found several species of gonolobus, which are twining herbs of little beauty. Among cultivated exotics of this family are the wax plants (Hoya carnosa and other species), with fleshy oval leaves and umbels of beautiful but artificial-looking flowers; Stephanotis floribunda, one of the most valued greenhouse climbers, with fine foliage and pure white fragrant flowers; and the singular stapelias, with cactus-like stems and lurid flowers with the odor of carrion.
Common Milkweed (Asclepias Conrati). - 1. Flower. 2. Pollen Masses. 8. Pod. 4. Seeds imbricated on the placenta.
Variegated Milkweed (Asclepias variegata).