Page:Encyclopædia Britannica, Ninth Edition, v. 4.djvu/108

a thickened or flattened appearance, as is seen in the Fir, Ash, and other trees. These fasciated branches, in some cases, however, are owing to the abnormal development of a single bud. Occasionally adventitious buds are produced on the edges of leaves, .is in Bryophyllum calyciimm (fig. 67), Malaxis paludosa, and various species of Asplenium, and on the surface of leaves, as in Or- uithogalum thyr- Boideum. These are capable of forming indepen dent plants. Simi lar buds are also made to appear on the leaves of Ges- nera, Gloxinia, rt Ap1iimpnp& m ALmweiieb, uy wounding various parts of them, and placing them in moist soil ; this is the method often pursued by gardeners in their propagation. The Ipecacuan plant has been propagated by means of leaves inserted in the soil. In this case the lower end of the leaf becomes thickened like a conn, and from it roots are produced, and ultimately a bud and young plant.

Leaves bearing buds on their margin are called proliferous.

lt;5 Viv Leaf of Bryophyllum calycinum, producing buds along the margil]i ftt Ul(J ex t r e m itics of the primary veins.

Fig. 68.

Rhizome r of Polygonatum muUiflorum (Solomon s Per Watpr-lilv manv Seal ). forming buds and adventitious roots, a, yo bud . ^ lmd (lcvel()pcd as a tranch . ,

cicatrices or scars of old branches.

Fig. 69.

Fig. 70. FIG. 69. Corm of Meadow Saffron (Colchicum autumnale). a, old conn shrivel ling; b, young corm produced laterally from the old one. Fio. 70. Corms of Colchicum autumnale in autumn when the plant is in flower.

• , oldest corm ; h, h, brown scales covering it; u>, its roots ; si, its withered flower

ing stem; k , younger conn produced from k; wA, roots from A- , which grows at expense of i; i, s , t", sheathing leaves; I ,i", foliage leaves; b, b, flowers; k", young corm produced from k in autumn, and which in succeeding autumn will produce flowers. (Sachs.)

The typical form of stems is rounded. They are some

times compressed or flattened laterally, while at other times they are angular : being triangular, with three angles and three flat sides ; trigonous, with three convex faces ; triquet rous, with three concave sides ; quadrangular or square ; quinquangular or five-angled ; octangular or eight-angled, &c. Various terms are applied to the forms of stems, as cylindrical or terete, jointed or articulated, &c. The fol lowing are some of the more important modifications of stems : The crown of the root is a shortened stem, often partially under ground, which remains in some plants after the leaves, branches, and flower-stalks have withered. In this case the internodes are very short, and the nodes are crowded together, so that the plant appears to be stemless. It is seen in perennial plants, the leaves of which die down to the ground annually. A rhizome or root-stock (fig. 68) is a stern which runs along the surface of the ground, being partially covered by the soil, sending out roots from its lower side and leaf-buds from its upper. It occurs in Ferns, Iris, Hedychium, Acorua Or Sweet Flag, Gin- gei, yvaiei my,many Species of CareX, Rushes, Anemone, Lathraea, <fec. By many the term rhizome is applied to stems creeping horizontally, whether they are altogether or only partially subterranean. In rhizomes called definite, the terminal bud gives off flowers, and the lateral buds form the stem ; while in indefinite rhi zomes the terminal leaf-bud is formed annually. A rhizome such as occurs in Solomon s Seal (fig. 68) is not a single stem, i.e., the product of a single bud, but is composed of por tions of successive axes, the leaves of which have died off and remain as scars (fig. 68, c, c); it is thus an indefinite rhizome. Rhizomes are well seen in British Ferns. A rhizome sometimes assumes an erect form as in Scabiosa succisa, in which the so-called prcemorse root is in reality a rhizome, with the lower end decaying. The erect rhizome of Cicuta virosa shows hollow internodes, separated by partitions. A pseudo-bulb (fig. 62) is an enlarged bulbous-like aerial stem, common in Orchidaceous plants. It is succulent, often contains numerous spiral cells and vessels, and is covered with a thick epidermis. A soboles is a creeping- underground stem, sending roots from one part and leaf- buds from another, as in Couch-grass, Carex arenaria, and Scirpus lacustris. It is often called a creeping root, but is really a rhizome with narrow elongated internodes. A. tuber is a thickened stein or branch produced by the approximation of the nodes and the swelling of the inter- nodes, as in the Potato. The eyes of the Potato are leaf- buds. Tubers are sometimes aerial, occupying the place of branches. The ordinary herbaceous stem of the Potato, when cut into slips and planted, sends off branches from its base, which assume the form of tubers. Tubers frequently store up a quantity of starch as in Marauta arundinacea, whence arrowroot is derived. Another form of thickened underground stem is the corm, as seen in the Autumn Crocus (Colchicum, fig. 69), Gladiolus, &c. Structurally it is composed of a solid more or less rounded axis covered by a layer of thin membranous scales (fig. 70, h, h). A corm is only of one year s duration, giving off buds annually in the form of young corms. In autumn the young corm gives origin to leaves, the lower of which (s, s , s") form sheaths round the corm and flower-stalk, the upper (I , I"} re maining very small ; and in the axil of the uppermost leaves the flowering-stem develops and bears the flowers (b, b ). Meanwhile in the axil of the middle leaves on the corm, a bud the rudiment of a new corm appears (k"). The flowering-stem dies down, and the corm from which it arose enlarges greatly during the winter at the expense of its parent corm (k), which thus becomes shrivelled. In spring the leaves produced on it (/ , I"), which were merely

rudiments in autumn, appear above ground as conspicuous