The botanist draws a distinction between a prickle and a thorn. A prickle can be removed with ease from the stem or leaf on which it grows. It is not incorporated with the wood, but merely, and often very lightly, attached to the bark or to the surface or edge of the leaf.
A thorn is, on the contrary, a fixture. The woody fibre of the plant runs up into it, and it cannot be detached without considerable difficulty.
Fig. 92. - Common wild teasel (Dipsacus sylvestris).
The gorse (Fig. 92), the hawthorne, and the orange-tree are guarded by thorns indeed. But the so-called "thorns" which mar our delight in the queen of flowers are in reality prickles, and so are the natural defences of the blackberry and the thistle.
Further south, where life teems, under a semi-tropic sun, and the struggle for existence is keen in proportion to the number of the organisms engaged in it, many plants are provided with defensive and even offensive weapons, which make them formidable to all who venture too near. The cactus, for instance, is a succulent plant, growing on-sandy plains, glaring rocks, or shining beaches, where such juicy stalks would be peculiarly grateful to parched throats; and it is dotted all over its surface with dense clusters of small but very penetrating and poisonous prickles. The pineapple, another refreshing thing native to thirsty lands, has foliage like the cheval-de-frieze of mediaeval warfare. The fruit "sits," as its southern cultivators might say, in the midst of a ring of erect sword-shaped leaves, every one of which is bordered, for its entire length, along both edges, with sharp thorns. The pineapple gatherers are obliged to work in leathern boots reaching to their hips, and without this defence the toothed leaves would rend clothing to ribbons, and cruelly tear the flesh beneath. In the saw-palmetto of the Florida "flat-woods," every leaf-stem is protected on both sides with curving points like the teeth of a saw.
Fig. 92. - Irish gorse, furze, or whin (Ulex Europceus).
The stings of our nettles are decidedly unpleasant, but they are not to be compared for a moment to the sufferings which can be inflicted by some tropical species. Listen, for instance, to De La Tour's experiences with an East Indian nettle. "One of the leaves," he says, "slightly touched my hand. At the time I experienced a slight pricking. The pain increased. In an hour it had become intolerable, as if some one was rubbing my hand with a red-hot iron. The pain spread rapidly along my arm as far as the armpit. I did not finally lose the pain for nine days".
Even our comparatively innocent nettle has one of the most highly developed of all the devices by which familiar plants guard themselves against the attacks of animals. Its sting is a tiny hollow cone, with the point upward. At the base of this are a number of cells filled with an irritating fluid containing formic acid, the same poison which gives virulence to the bites of the ant and the spider. And at the tip of the cone is a small round disk set on slantwise. When the sharp point of the cone is touched, however gently, it pierces the skin. Then the disk breaks off, and the poison which is in the cells at the base of the sting is pressed up through the hollow cone and into the wound. If a browsing cow thrusts her tender nostrils into a nettle-clump the points pierce her skin, the poison enters her veins, and she receives a sharp warning to let nettles alone in future.
We have several varieties of nettle, all immigrants from the old world. Their flowers are modest little green affairs, so inconspicuous that most people do not believe nettles ever bloom at all. These tiny blossoms are borne on short branched spikes, which grow out almost at right angles to the leaf-stalks, and are often half hidden by the leaves. Each spike is made up of separate green blossoms, with four tiny flower-leaves apiece.
Some of the wee flowers bear stamens only, some bear pistils only, and, as a rule, both sorts of flower grow on one plant, though not unfrequently we come across a nettle whose blossoms are all of one kind. The stamen-heads explode when the bud expands, scattering the pollen, which is borne from flower to flower, or from plant to plant, by the wind. As the nettles have hence no need to attract insects, the little blossoms have no petals whatever, only four small greenish sepals.
The florets which bear stamens only have in their midst a little green affair which is the reminiscence of a pistil. But the pistil now in use has a whole flower to itself, and is surrounded by two pairs of sepals (Fig. 93), the outer couple small and spreading, the inner broader and upright. At the tip of the pistil there is a scattered tuft of hairs, to catch any chance pollen blowing by.
Fig. 93. - Single blossoms of the nettle.
a, Staminate flower just expanding; 6, fully opened staminate flower; c, pistillate flower.
The nettle is connected with much wonder-lore, folk-lore, and tradition. Moreover, the family in times gone by has been not only famous, but useful. Its name is derived from the passive participle of a verb common to most Indo-European Ianguages which means "to sew." Closely allied words are "needle," "net," and "knit." Nettle would seem to mean "that with which we sew," and indicates that this plant supplied the thread used in former times by the German and Scandinavian nations. "We know this to have been a fact," says Moncure D. Conway, " in the Scotland of the last century. Scotch cloth is only the housewifery of the nettle; and a fabric made from the fibres of the plant was also used till a recent period in Friesland." Flax and hemp bear southern names, and when they were brought into the north of Europe the nettle's career of usefulness was ended. Like handicraftsmen on the introduction of machinery, it was thrown out of honorable employment. Then it became a vagabond and took to roadsides and wastes. Nettles are said to have been introduced into England by Roman soldiers who sowed the seed in Kent for their own use "to rubbe and chafe their limbs when through extreme cold they should be stifle and benumbed," having been told that the climate of Britain was so cold that it was not to be endured without some friction to warm their blood.