OF THE STEMS AND STALKS OF PLANTS.
Botanists reckon seven kinds of stems or stalks of plants.
1. Caulis, a stem, fig. 9. properly so call ed, bears both leaves and flowers, as the trunks and branches of all trees and shrubs, as well as of many herbaceous plants besides. By its means the organs of plants are raised to a commodious height above the ground, and presented in various directions to the atmosphere and light. In germination, it always takes a contrary direction to the root. As it advances in growth, it is either able to support itself; or twines round or ad heres to other bodies. Some stems creep on the ground, and take root here and there, by which the plant is increased. The stern is either simple, as in the lily, or branched, as in the generality of plants. When regularly and repeatedly divided, with a flower springing from each divi sion, it is called midis dichotomus a fork ed stem. Though generally leafy or scaly, a stem may be naked in plants destitute of leaves altogether, as the creeping cereus, and the genus staphe lia. Climbing stems are of several kinds ; as radicans, clinging to any other body for support, by means of fibres which do not imbibe nourishment; scandens, climb ing by means of spiral tendrils, like the vine and passionflower; odubi/is, twin ing round any thing that comes in its way by its own spiral form, either from left to right, according to the apparent motion of the sun, like the honeysuckle; or from right to left, like the convolvo lus and French bean ; nor can any art or force make a twining stem turn contrary to its natural direction. In the manner of their growth and branching sterns are very various, being either straight, irre gularly spreading, or zigzag either al ternately branched or oppositely ; two ranked, when the branches spread in two horizontal directions; or brachiate, four ranked, when they spread in four direc tions, crossing each other alternately in pairs. Caulis determinate ramosus, an ab ruptly branched stem, belongs particu larly to the heaths, the rhododendron, &c. and is a term invented by LinnNus to express their peculiar mode of growth ; each of their branches, after terminating in flowers, throws out a number of fresh ascending shoots from just below the flowering jointed The Indian fig has a re markable ointed stem, whose ovate por tions look like leaves ; possibly the scales with which they are covered may be equivalent to leaves.
The shape of a stem is either round or two•edged, as in the everlasting pea, or with three, four, or more angles. Square stems are extremely common, and such generally bear opposite leaves. Several stems are winged, the angles being extended into leafy borders, as in thistles.
The surface of the stem is either smooth, rough, watery, viscid, bristly, hairy, downy, woolly, hoary, or glaticous It is either striated with fine parallel lines, or more deeply furrowed ; sometimes it is spotted with a purplish hue.
The inner part of the stem is either solid, in which case its centre is occupied with pith ; or hollow, and lined with a white shining membrane, of which the hemlock is an example. When the stem is want ing, a plant is called acaulis, as is the case with the daisy and primrose. The nature of the stern agrees in many respects with the caudex, or body of the root, at least in trees and shrubs ; for such are capable of being propagated by cuttings of their stem or branches, which, when planted, throw out roots. This is not the case, however, with annual stems. Linnxus calls the stems of trees roots above ground. It is frequently indifferent which end of a cutting is planted in the earth; and the extremity of a branch bent down to the ground in most cases readily takes root, which circumstances confirm his idea.
The stem of several plants is subjectto a disease, whence it becomes as it were compound or clustered, forming a broad flat figure, crowded with leaves or flow ers at the extremity, and sometimes be sprinkled with them at the sides. We have seen it in the ash, holly, broom, nasturtium, wall-flower, toad-flax, &c. A kind of pea is frequently cultivated in Norfolk with red and white flowers, and a tender eatable pod, called the top-knot pea, in which this variety of stem is regu larly propagated by seed.