History—The use as a purgative of the tuber of a convolvulaceous plant of Mexico, was made known by the early Spanish voyagers; and so highly was the new drug esteemed that large quantities of it reached Europe during the 16th century.
Monardes, writing in 1565, says the new drug was called Ruybarbo de las Indias or Ruybarbo de Mechoacan, the latter name being given in allusion to the province of Michoacan whence the supplies were derived. Some writers have advanced the opinion that mechoacan root was the modern jalap, but in this we do not concur, for the description given of mechoacan and the place of its production do not apply well to jalap. Both drugs were moreover well known about 1610; they were perfectly distinguished by Colin, an apothecary of Lyons (1619), who mentions jalap (“racine de Ialap”) as then newly brought to France.[1635] They were however often confounded, or at least only distinguished by their difference of tint. Thus jalap, which at that period used to be imported cut into transverse slices,[1636] was termed, from its darker colour, Black Mechoacan; and on the other hand, the paler mechoacan was in later times known as White Jalap.
Mechoacan root is now known to consist (at least in part) of the large thick tuber of Ipomœa Jalapa Pursh (Batatas Jalapa Choisy), a plant of the Southern United States and Mexico. As a drug it has been long obsolete in Europe, having given place to jalap, which is a more active and efficient purgative.
The botanical source of jalap was not definitely ascertained until about the year 1829, when Dr. Coxe of Philadelphia published a description and coloured figure, taken from living plants sent to him two years previously from Mexico.[1637]
Manner of Growth—Though we have cultivated the jalap plant for many years, we have had no opportunity of examining the seedling, but judging from analogy suppose that it has at first a small tap-root which gradually thickens after the manner of a radish. A root of jalap, called by some tuber and by others tubercule, throws out in addition to aerial stems, slender, prostrate, underground shoots which emit roots at intervals. These roots while but an inch or two long become thickened and carrot-shaped, gradually enlarging into napiform tuber-like bodies, which emit a few rootlets from their surface and taper off below in long, slender ramifications. The thickened roots have no trace of leaf-organs; the aerial stems grow from the shoot from which they originated.
Fresh jalap roots (tubers) are externally rough and dark brown, internally white and fleshy.
Collection—Jalap is said to be dug up in Mexico during the whole year.[1638] The smaller roots are dried entire; the larger are cut transversely, or are gashed so that they may dry more easily. As drying by sun-heat would be almost impracticable owing to the wetness of the climate, the roots are placed in a net, and suspended over the almost constantly burning hearth of the Indian’s hut, where they gradually dry, and at the same time often contract a smoky smell. Much of the jalap that has of late arrived has been more freely sliced than usual, and has obviously been dried with less difficulty.
According to Schiede, whose account was written in 1829,[1639] the Indians of Chiconquiaco were at that period commencing the cultivation of jalap in their gardens.
Description—The jalap of commerce consists of irregular, ovoid roots, varying from the size of an egg to that of a hazel-nut, but occasionally as large as a man’s fist. They are usually pointed at the lower end, deeply wrinkled, contorted and furrowed, and of a dark brown hue, dotted over with numerous little, elongated, lighter coloured scars, running transversely. The large roots are incised lengthwise, or cut into halves or quarters, but the smaller are usually entire. Some of the small roots are spindle-shaped or cylindrical; others can be found which are nearly globular, smooth and pitchy-looking, but these latter are seldom solid. Good jalap is ponderous, tough, hard and often horny, becoming brittle when long kept, and breaking with a resinous non-fibrous fracture; internally it is of a pale dingy brown or dirty white. It has a faint smoky, rather coffee-like odour, and a mawkish taste, followed by acridity.
Microscopic Structure—Seen in transverse section, jalap exhibits no radiate structure, but numerous small concentric rings, which in many pieces are very regularly arranged. They are due to the laticiferous cells, differing from the surrounding parenchyme only by their contents and rather large size. These laticiferous cells traverse the tissue in a vertical direction, constituting vertical bands, as may be observed on a longitudinal section; the single cells are simply placed one on the other, and do not form elongated ducts as in Lactuca or Taraxacum.