The Structure of Plants

The propagation Culture and management of horticultural plants are based to a considerable extent upon a knowledge of the structure units of the plant, which are known as organs, are the roots, stems, laves, flowers, and fruits. Each is composed of several defer ant kinds of tissue, such as xylem, Phloem, and cambium, and this tissues, in turn, are composed of cells. Some cells have thick walls, others have thin walls; cells differ also in size, shape, and cell contents. The three principal types of cells in plants are parenchyma, and collenchymas.
Roots :
The roots are essential organs of most plants. The chief functions of roots are to absorb moisture and nutrients for the plant and to provide anchor for it. The following kinds of roots may be conveniently considered from the standpoint of origin, structure, and function
Primary roots :
The radical of a germinating seed produces the first foot of the new plant. This is the produces the first root of the new plant. This the primary root produces the so-called ‘taproot.’ In some plants, as walnut and hickory, the growth of the taproot  predominates for several years, and they are commonly regarded as tap rooted
Plants :
Secondary and Lateral Roots. Branch roots that arise from the taproot are known as secondary foots is horizontal. Roots that develop laterally on any previously fumed root roots are known as lateral roots. In reality, may develop from the taproot, from other lateral roots, or in some cases from stems. There is considerable variability in the extent of branching shown by roots of different species of plants. The tomato is an example of a plant in which free branching occurs; root branching in the onion, on the contrary occurs less freely; and the hyacinth produces roots that are normally unbranched.
The peach and apple are examples of plants is which there is limited development the taproots but extensive development of the lateral-rooted roots. Plants in which this occurs are known as lateral-rooted plants. The spread an depth of the root system and the extent of branching in poor soil. Hence plants in sandy soil of low fertility tend to produce long rots with relatively few branch roots.
As the radical of the germination seed begins to grow, it consists initially of primary cells which form primary tissues. As it and the branch roots that develop from it continue to grow, the region extending a short distance from the tips is characterized by primary growth. Branch roots arise from the epicycle tissue, at a postal ways shortly back of the growing tip. The youngest roots are always nearest the  tip of the root, and the older ones are toward the base. Since they thus develop in regular succession, they are known as regular or acropolis roots.
Adventist Roots :
Those that arise from other tissue and organs of the plant than the percycel of young roots are called varying degree of readiness, from toots, stems, leaves, and modified part of the principal kinds of horticultural plants They never, or rally, from the stems of certain onse; they form readily from the roots and stems of some dicotyledonous plants, but les readily from other; they form quite readily plants, but not from gymnosperms. The tissue from which adventives roots originate are principally the cambium, and callus of stems, and the parenchyma tissue near cambium of vascular bundles of leaves.
Root Hairs :
Simple, hair like outgrowths of the outer walls of cells of the epidermis of the root are produced by many plants. These are known as root hairs. They grow out into space between soil particles and absorb moisture and nutrients for the plant. Most of the higher vascular plants, such as peach, apple, grapefruit, cranberry, and pecan, do not have normal root hairs, at least under certain soil conditions. With these the absorption of moisture is performed by various small lateral roots. They function for a short time as absorbing organs; then they either die or begin secondary growth and become part of the permanent root  which consist of primary tissue, it is obvious that the root hairs occur only on the terminal portion of young growing roots. Root hairs normally function only during a relatively short period. As they wither and disappear, others develop near the terming growing point of the root.

0 comments:

Post a Comment