Anatomy of Flowering Plants Test - 28

Intrafascicular/intrastelar cambium is present between xylem and phloem in dicot stem and roots. Pith rays, present between the edges of intrafascicular cambium, divide to form a new cambium strip between the two vascular bundle i.e. interfascicular cambium. Thus, inter and intra fascicular cambium together forms a complete cambium ring, called as vascular cambium, which forms secondary xylem on inner side and secondary phloem on outer side. Differential cambial activity during autumn and spring season result in narrow and wide secondary xylem rings respectively, which together forms the annual growth ring. 

Cork (phellem) is a non-living, water-resistant, protective tissue that displaces the stem epidermis as the plant undergoes an increase in diameter during the secondary growth phase. Cork is an external, secondary tissue impermeable to water and gases. It serves as protection against damage, parasites and diseases, as well as dehydration and extreme temperatures. The epidermis cell is a single layered group of cells that covers plants leaves, flowers, roots and stems. It forms a boundary between the plant and the external environment.
The epidermis serves several functions, it protects against water loss, regulates gas exchange, secretes metabolic compounds and absorbs water and mineral nutrients. It is also an external protective tissue.
The cortex is the outermost layer of the stem or root of a plant, bounded on the outside by the epidermis and on the inside by the endodermis. It is responsible for the transportation of materials into the central cylinder of the root through diffusion and may also be used for food storage in the form of starch. The pericycle is a cylinder of parenchyma or sclerenchyma cells that lies just inside the endodermis and is the outer most part of the stele of plants. 
Thus, the correct answer is option D.

Dicot root vascular bundles are described as radial and tetrarch. There are four bundles each of xylem and phloem occurring alternately. Xylem is described as exarch. 

More distinct annual rings are formed in that regions, where climatic variations are sharp. More distinct annual rings are formed in temperate plants. Distinct annual rings are not formed in tropical plants. Distinct annual rings are not formed in India except Himalayan regions. Least distinct annual rings are formed in seashore regions because the climate remains same throughout the year. More clear annual rings are formed in deciduous plants as compared to evergreen plants. In temperate region),  in deserts annual rings are less distinct. Annual rings are bands of secondary xylem and xylem rays. Sometimes drought conditions prevail during the middle of a growing season resulting in formation of more than one annual ring. These are called pseudo annual rings. Thus, option C is correct.

Phellogen is defined as the meristematic cell layer responsible for the development of the periderm. Cells that grow inwards from the phellogen are termed phelloderm, and cells that develop outwards are termed phellem or cork. The periderm is the secondary protective (dermal) tissue that replaces the epidermis during growth in thickness of stems and roots of gymnosperms and dicotyledons. 
Thus, the correct answer is option B.

More distinct annual rings are formed in that regions, where climatic variations are sharp. More distinct annual rings are formed in temperate plants. Distinct annual rings are not formed in tropical plants. Distinct annual rings are not formed in India except Himalayan regions. Least distinct annual rings are formed in seashore regions, because the climate remains same throughout the year. 

Most monocots either have no secondary growth or else anomalous secondary growth of some type. For example, palm trees increase their trunk diameter due to division and enlargement of parenchyma cells, which is termed as 'diffuse secondary growth'. In some other monocot stems with anomalous secondary growth, a cambium forms but it produces vascular bundles and parenchyma internally and just parenchyma externally. Some monocot stems increase in diameter due to the activity of a primary thickening meristem, which is derived from the apical meristem. Stem of date palm increases in girth due to activity of apical meristem and not because of intercalary meristem and lateral meristem (involves in normal secondary growth of dicots). Thus, option B is correct.

Secondary growth refers to the growth that results from cell division in the cambia or lateral meristem and that causes the stems and roots to thicken, while primary growth is growth that occurs as a result of cell division at the tips of stems and roots, causing them to elongate and gives rise to primary tissue. Secondary growth occurs in most seed plants, but monocots usually lack secondary growth. In many vascular plants, secondary growth is the result of the activity of the two lateral meristems, the cork cambium and vascular cambium. Arising from lateral meristems, secondary growth increases the girth of the plant root or stem, rather than its length. As long as the lateral meristems continue to produce new cells, the stem or root will continue to grow in diameter. Thus, option A is correct.