Of the vegetable sting-bearers none are more familiar to us than the Nettle, three species of which inhabit this country. The two commonest are the Great Nettle (_Urtica diœcea_) and the Small Nettle (_Urtica urens_), and both of them are armed with venomous stings, which cause the plants to be so much dreaded. The structure of these stings is very simple, and can be made out with an ordinary microscope, or even a good pocket lens. Each of these stings is, in fact, a rather elaborately constructed hair, hollow throughout its length, coming to a point at the tip, and having the base swollen into a receptacle containing the poisonous juice. When any object--such, for example, as the human hand--touches a nettle, the points of the stings slightly penetrate the skin, and the hair is pressed downwards against the base, so that the poison is forced through the hole. One of these hairs is shown in the left-hand bottom corner of the illustration. Even the tiny stings of our English nettles are sufficiently venomous to cause considerable pain, and, in some cases, even to affect the whole nervous system. But some of the exotic nettles are infinitely more formidable, and are, indeed, so dangerous that, when they are grown in a botanical garden, a fence is placed round them, so as to prevent visitors even from touching a single leaf. The two most dreaded species are called _Urtica heterophylla_ and _Urtica crenulata_. The former is thought to be the more dangerous of the two, and a good idea of its venomous qualities may be gathered from an account of an adventure with _Urtica crenulata_. The narrator is M. L. de la Tour. “One of the leaves slightly touched the first three fingers of my left hand; at the time I only perceived a slight pricking, to which I paid no attention. This was at seven in the morning. The pain continued to increase, and in an hour it became intolerable; it seemed as if some one were rubbing my fingers with a hot iron. Nevertheless, there was no remarkable appearance, neither swelling, nor pustules, nor inflammation. “The pain spread rapidly along the arm as far as the armpit. I was then seized with frequent sneezing, and with a copious running at the nose, as if I had caught a violent cold in the head. About noon I experienced a painful attack of cramp at the back of the jaws, which made me fear an attack of tetanus. I then went to bed, hoping that repose would alleviate my suffering, but it did not abate. On the contrary, it continued nearly the whole of the following night; but I lost the contraction of the jaws about seven in the evening. “The next morning the pain began to leave me, and I fell asleep. I continued to suffer for two days, and the pain returned in full force when I put my hand into water. I did not finally lose it for nine days.”