Stem

In the germination of a seed the plumule produces the first stem of the new plant. The continued growth for one or more seasons of this first stem and, in most species, the branching of it produce the trunk and framework of the new plant. Stems, in turn, produce the buds, leaves, flowers, and fruit. They also serve as conducting systems for water and nutrients between the roots, leaves, and fruit. The principal groups of horticultural plants are angiosperms and gymnosperms.

Monocotyledonous Plants :

In general str4ucture the stem of these plants consist of a terminal growing point, nodes, buds, and internodes. In cross section the stem consists of epidermis, perhaps a cylinder of thick-walled schlerenchyma beneath the epidermis, and isolated vascular bundles distributed in a mass of fundamental tissue similar to the pith of dicotyledons. The internodes of monocotyledonous plants provide most of the length growth of the stem. The lower part of each internodes is region of elongation. This in part accounts for the exceedingly rapid length growth of stems of certain monocotyledonous  plants, such as the bamboo, Johnson grass, and asparagus.

The elongation of the stem many continue for many years. The date palm, for example, lives for an indefinite period and may ultimately grow to be 50 feet high, corm, on the country, survives only one season and rarely grows taller than 6 to 8 feet. In some species the terminal growing point produces the inflorescence of the plants. This is true of the onion, and also of corn, which produces the tassel terminally on the main stalk and the postulate inflorescence  on a lateral branch.

The nodes of monocotyledons sometimes give rise to auxiliary buds Such buds are rare on the date palm, with the result that the plants normally produce single entrenched stems with only occasional offshoots. Corn, on the contrary produces buds freely at the nodes, some of which grow into branch stems while others produce the ears of corn.

Dicotyledonous and Gymnosperm Plants :

Young stems of these plants have a pith, xylem, cambium, phloem, epicycle endodermis, cortex, and disappeared, and exposed phloem cells form a perineum, or bark. Stems of dicotyledons make terminal growth by elongation of cells near the tip of a growing branch. the terminal growing point in its process of growth may (1)  produce a terminal bud, from which growth will be4 resumed the following season,  (2)  produce a terminal inflorescence as in the gape, apple, pecan, walnut, cabbage, and carrot, or (3) it may about , in which case future growth of the stem will be from an axillary’s bud below.

Young in the process and development differentiate into nodes and inter nodes. Leaves and buds are normally formed at nodes. The area between nodes is known as the interned. The inter nodes in stems e very short, as in cabbage, or relatively long, as in the grape, depending on the species. Rapidity of growth caused by growing conditions also influences the length of the inter nodes of many species.

The cambium layer of stems of these plants is of peculiar interest and concern because of its relationship to several important horticulture practices and treatments. Briefly, the cambium layer serves the plant in these ways; (1) It is the systematic tissue responsible for increase in size of the stem after it begins secondary growth . Cambium cells occur in a continuous ring between the xylem and phloem. During each season of growth they enlarge and divide and differentiate into now xylem cells toward the inside and now phloem cells toward the side. If the cambium fails to function because of mechanical injury or physiological causes, no xylem and phloem are formed. Since these tissue are essential to the normal growth of a plant, death results if the activity of the cambium layer is restricted for a prolonged period. The healing of wounds is made possible by the cambium layer and is accomplished by two processes, Regeneration may take place where bark is removed and living cambium cells are exposed on the surface of the wood. Under the favorable conditions of high humidity and warm temperature such cells may become active and reconstruct new tissues on the surface of the wound. New growth from these cells is outward in a radial direction. Over walling takes place as a result of the growth in a lateral direction of cambium cells around the margins of a wound, causing now tissue to advance from various sides to cover the wound.(3) The cambium produces callus tissue which is essential to the success of budding and gifting. Callus also forms on the cut ends of cuttings of some plants. This may provide   protection against decay-producing organisms. In tare cases, roots arise directly from the callus tissue, though in most cases they arise directly from the callus tissue, though in most cases roots they arise directly from the callus tissue, though in most cases thy arise directly from the cambium and callus is not essential tooting. (4) Finally, when adventitious roots develop on stems or on contained cells near the cambium.