Anatomy of Flowering Plants Test - 21

Collenchyma tissue is composed of elongated cells with irregularly thickened walls. They provide structural support, particularly in growing shoots and leaves. Collenchyma tissue makes up things such as the resilient strands in stalks of celery. Collenchyma cells are usually living and have only a thick primary cell wall made up of cellulose and pectin. Cell wall thickness is strongly affected by mechanical stress upon the plant. Collenchyma cells are most often found adjacent to outer growing tissues such as the vascular cambium and are known for increased structural support and integrity. So, the stems of few dicot plants are getting mechanical strength mainly because of collenchyma before secondary growth. Parenchyma is a versatile ground tissue that generally constitutes the filler tissue in soft parts of plants. It forms, among other things, the cortex and pith of stems, the cortex of roots, the mesophyll of leaves, the pulp of fruits, and the endosperm of seeds. Sclerenchyma is the supporting tissue in plants after secondary growth. 
Thus, the correct answer is option B.

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. Although it is composed of non-vascular parenchyma cells, it is still considered part of the vascular cylinder, because it arises from the procambium as do the vascular tissues it surrounds. 

• Secondary growth does not occur in a monocot plant because of the absence of cambium in a vascular bundle in between xylem and phloem.
• But in monocots like Dracaena Secondary growth is seen. Only in some exceptional cases but it is rare
• Hence, No secondary growth appears in monocot roots, because They lack cambium.
• So, the correct answer is 'They lack cambium.'.

Intercalary meristem at base of leaves or nodes of grasses is responsible for  primary growth. Meristems are classified by their location in the plant as apical located at root and shoot tips, lateral in the vascular and cork cambia, and intercalary at internodes or stem regions between the places at which leaves attach, and leaf bases. Intercalary meristem cells possess the ability to divide and produce new cells, as do apical and lateral meristems. They differ, however, in being situated between regions of mature tissue, such as at the base of grass leaves, which are themselves located on mature stem tissue.
Therefore, the correct answer is option A.

Hypodermis is a region lying immediately below the epidermis. It is represented by a few layers of collenchyma cells with angular thickenings in dicot stem. The cells are compactly arranged without any intercellular spaces. Hypodermis provides mechanical support and additional protection. Thus, option A is correct. 

• A meristem may be defined as the group of cells which divide continuously to give rise to new cells. 
• A meristem is the tissue in most plants containing undifferentiated cells, found in zones of the plant where growth can take place. 
• Meristematic cells give rise to various organs of the plant and keep the plant growing. 
• Meristematic cells are incompletely or not at all differentiated and are capable of continued cellular division. Furthermore, the cells are small and protoplasm fills the cell completely. The vacuoles are extremely small. 
• The cytoplasm does not contain differentiated plastids, although they are present in rudimentary form- proplastids. 
• Meristematic cells are packed closely together without intercellular cavities. 
• The cell wall is a very thin primary cell wall.

In monocot root, vascular bundles are radial in arrangement. There are eight bundles each of xylem and phloem. Hence, the condition is described as polyarch. Xylem is described as exarch. 

Net-veined leaves, annual rings and seed with two masses of stored food are characteristic features of dicots. 

Lysigenous intercellular spaces is type of intercellular space arises through dissolution of entire cells, which are therefore called as lysigenous cavity. These cavities of intercellular spaces store up water, gases and essential oils in them. The examples are commonly found in water plants and many monocotyledonous stems. The secretory cavities in Eucalyptus, Citrus and Gossypium are good examples. In monocot stem  the vascular bundle encloses both xylem and phloem. Xylem is found towards the inner surface and phloem towards the outer surface. Cambium is absent. Hence, the vascular bundles are described as conjoint, collateral and closed. In the xylem, there are two metaxylem and two protoxylem vessels arranged in the shape of Y. 

Eustele - In this arrangement, the primary vascular tissue consists of vascular bundles, usually in one or two rings around the pith. In addition to being found in stems, the eustele appears in the roots of monocot flowering plants. The vascular bundles in a eustele can be collateral with the phloem on only one side of the xylem or bicollateral with phloem on both sides of the xylem, as in some Solanaceae. So, eustele is the characteristic of monocots and absent in dicots, pteridophytes and bryophytes. 
Thus, the correct answer is option A.