datura, and deadly night-shade. Among the Cinchonacece, the true Cinchonas are too well known for their febrifuge properties to require further notice, except that in pro- portion to the number of species yielding medicinal bark, is the difficulty of assigning to any particular species, those kinds which are officinal. But in countries where the true Cinchonas do not exist, others of this family are used as substitutes, as Pinckneya pubens in Carolina, Portlandia heceandra in French Guiana, Rondeletia febri- fuga in Sierra Leone ; so also Macrocnemum corymbosum, Guettarda coccinea, Antirrhoea verticillata, Morinda Royoc, and others ; with Hymenodictyon excelsum in India.
Of the Convolvulacece, Ipomcea Jalapa of Nuttal yields the true jalap, and Convolvulus Scammonia, scammony; so in India, Ipomcea Turpethum forms the toorbud of the Arabs, probably corrupted from the Sanscrit trivrit ; and the seeds of Ipomcea caerulea, described by Mesue under the name of hub-al-nil and granum indicum, are still used in India for their purgative properties. In the Cucurbitacece there exists a bitter principle in the fruit of many species ; and in the rind of the cucumber and the melon. Of this family, colocynth, squirting cucumber, and bryony, are used as purgatives ; in India, with the true colocynth, there is a nearly allied species substituted for it, which I have named Cucumis pseudo-Colocynthis ; some other species of this genus, as well as of Trichosanthes, Luffa, and Lagenaria, are likewise used as purgatives.
In connexion with this subject may be mentioned a discovery to which I was led, entirely by inferences drawn from the natural affinities of plants. In a paper lately read to the British Association at Bristol, on the plants which yielded Caoutchouc, I observed that they all belonged to the milky-juiced families of Cichoracece, Lobeliacece, Apocynecs, Asclepiadece, Euphorbia cece, and Artocarpece, a tribe of Urticece. In the first place, it may be observed
