Botany and Plant Science

The endothecium is the layer of the anther wall that develops fibrous thickenings of callose, which help in the dehiscence of the anther to release pollen grains.

Each pistil is constructed of from one to many enrolled leaflike structures, or carpels, each of which encloses one or more ovules. The carpel is a single megasporophyll, or modified seed-bearing leaf. A pistil then may be composed of one carpel (simple pistil), as in the sweet pea, or of two or more carpels (compound pistil) partially or completely joined, as in the mustard (two carpels) or lily (three carpels). A carpel has three parts: stigma, ovary, and style. The stigma is responsible for pollination and is the top-most part of the carpel. The ovary is responsible for determining the number of carpels in a plant and is the bottom-most part of a carpel. Lastly, the style is responsible for connecting the stigma and ovary together, helping with the transfer of pollen through the carpel for pollination.

Gynoecium having a number of free carpels is called apocarpous.

The flowers belonging to the Papilionaceae family has vexillary type of aestivation in which, there is one large posteriorly placed petal called vexillum that overlaps the lateral petals called wings. These wings overlap the anterior petals that are fused to form a boat like structure called keel or carina. This type of aestivation is also called descending imbricate. These flowers also have an odd anterior sepal. They show piston mechanism of pollination. Their gynoecium is one carpel, it is monocarpellary, superior, unilocular with marginal placentation. For example, Pea, Dalbergia etc.

When ovary is lobed and the style emerges from the depressions of the lobes of the ovary, it is called gynobasic style. It is seen in the family Lamiaceae or Labiatae. 

Gynoecium with fused carpels is called syncarpous. Gynoecium with free carpels is called apocarpous.

A seed is an embryonic plant enclosed in a protective outer covering. The formation of the seed is part of the process of reproduction in seed plants, the spermatophytes, including the gymnosperm and angiosperm plants. The maturing ovule undergoes marked changes in the integuments, generally a reduction and disorganisation but occasionally a thickening. The seed coat formed from the two integuments or outer layers of cells of the ovule, which derive from tissue from the mother plant, the inner integument forms the tegmen and the outer forms the testa

Carpel is the female reproductive organ of a flower, consisting of an ovary, a stigma, and usually a style. A carpel is the female reproductive part of the flower, interpreted as modified leaves bearing structures called ovules, inside which the egg cells ultimately form. It may occur singly or as one of a group. Fertilization of an egg within a carpel by a pollen grain from another flower results in seed development within the carpel

Transfer of pollen grains to the stigma of a pistil is called pollination. Stigma is large and feathery so that it can trap air-borne pollen grains. 

The pistils of flowers are composed of carpels which contain many ovules that have seeds inside of them. Hence, a single pistil is capable of producing more than one ovule. 

Heterospory, seed formation and fertilization are found in gymnosperm. 

• Guard cells are cells surrounding each stoma. They help to regulate the rate of transpiration by opening and closing the stomata. 
• Lenticels are one of many raised pores in the stem of a woody plant that allows gas exchange between the atmosphere and the internal tissues. Bulliform cells are large, bubble-shaped epidermal cells that occur in groups on the upper surface of the leaves of many grasses. Loss of turgor pressure in these cells causes leaves to "roll-up" during water stress. 
• Subsidiary cell is a plant epidermal cell that is located next to a guard cell in the stoma of a leaf and differs in structure from other epidermal cells. Also called an accessory cell.

Promeristem are groups of meristematic cells found in germinating embryos or young seedlings. They give rise to primary meristems which initiate the organ formation process. Promeristems are also referred as primordial meristems or embryonic meristems because of their origin.
Thus, the correct answer is option A.

• In plants, receptacle or thalamus is a thick part of the stem from which the flower organs grow. Stipule is a small leafy outgrowth at the base of the leaf. The sepals of a flower that form a whorl enclosing the petals and forms a protective layer around the flowers.
• Carpels, on the other hand, is the female reproductive organ in a flower consisting an ovary, a stigma and probably a style. It produces egg cells and protects a developing baby plant.

Herbarium specimens are indeed poisoned to prevent fungal and insect attacks, but mercuric chloride (HgCl2) is typically used, not DDT. The other statements are standard practices for herbarium maintenance.