(a) Write an explanatory account of ethnobotany. Give a critical account of whether ethnobotany is a faith, myth or science…

(a) Ethnobotany: nature, scope, and whether it is faith, myth or science

What it is. J.W. Harshberger coined the term "ethnobotany" in 1895 for the study of plants used by aboriginal peoples. The field now studies the whole relationship between human cultures and plants: food, medicine, fibre, dyes, fuel, ritual, taboo, folk classification and the management of vegetation. It draws on botany, anthropology, linguistics, pharmacology and ecology. Richard Evans Schultes (Amazonian hallucinogens and medicinal plants) and Richard I. Ford shaped its modern form. In India, S.K. Jain of the Botanical Survey of India is regarded as the father of the discipline, and the All India Coordinated Research Project on Ethnobiology (AICRPE, from 1982) documented plant use among many tribal communities.

Scope and branches

• Ethno-medicine and ethnopharmacology: folk remedies as leads for drugs.
• Ethno-agriculture and food plants: landraces, wild edibles, famine foods, shifting cultivation.
• Ethno-ecology and conservation: sacred groves, such as the law kyntang of the Khasi in Meghalaya, the orans of Rajasthan and the devrais of Maharashtra, and totemic protection of trees.
• Ethno-taxonomy: how communities name and classify plants.
• Economic ethnobotany: fibres, gums, dyes, and intellectual-property and benefit-sharing issues.

Methods. Field surveys with prior informed consent, voucher herbarium specimens, and interviews with informants. Quantitative indices (use value, informant consensus factor, fidelity level) show how strongly a use is shared. Phytochemical and pharmacological tests then check a claimed activity.

Faith, myth or science: a critical assessment

Where it looks like faith or myth. Much folk plant knowledge is carried in ritual, taboo and belief. The doctrine of signatures held that a plant's shape shows its use (walnut kernel for the brain, liverwort for the liver). That idea has no scientific basis. Some remedies are ineffective, work only as a placebo, or are harmful. Aristolochia in herbal mixtures caused kidney failure and urothelial cancer. Claims are often vague about dose and plant part, and they vary from one informant to the next. Recording beliefs uncritically, or romanticising "traditional wisdom", turns ethnobotany into folklore.

Where it is science. Folk knowledge is itself the product of long trial and error, and it can be tested:

• Quinine from Cinchona bark, used by Andean peoples for fevers, became the first effective antimalarial.
• Reserpine from Rauvolfia serpentina (sarpagandha, used for "madness" and snakebite) became an antihypertensive and early tranquilliser.
• Artemisinin: Tu Youyou's team screened Chinese traditional remedies, and a 4th-century text by Ge Hong suggested cold extraction of Artemisia annua. Artemisinin became a first-line antimalarial, and she received the 2015 Nobel Prize.
• Jeevani: the Kani tribe of Kerala used Trichopus zeylanicus (arogyapacha) against fatigue. The Tropical Botanic Garden and Research Institute developed the anti-fatigue drug "Jeevani" from it and shared licence fees with the Kani, an early model of benefit-sharing that the Biological Diversity Act 2002 later formalised.
• Sacred groves: a religious taboo on cutting trees has in effect conserved relict forest, springs and wild genetic resources. Ecologists measure this.

Verdict. Ethnobotany is neither faith nor myth, though it studies both. The beliefs, taboos and myths around plants are its data. The discipline becomes a science when it documents those data systematically, frames testable hypotheses, and confirms or rejects them through chemistry, pharmacology and ecology. Only a small fraction of folk claims survive testing, and those few have given some of medicine's most important drugs. Its validity therefore rests on rigorous testing, not on the authority of tradition.

(b) Differentiation of xylem and phloem from cambial derivatives; vessel versus sieve element

The vascular cambium has two kinds of initials. Fusiform initials are long and tapering; they give rise to the axial (vertical) cells of xylem and phloem. Ray initials are short and roughly isodiametric; they give rise to the xylem and phloem rays. Periclinal divisions cut off derivatives on both faces. Those cut off towards the inside become secondary xylem; those cut off towards the outside become secondary phloem.

Comparison of the two pathways

• Amount: far more derivatives are added to the xylem side, often several times more than to the phloem, so wood forms the bulk of an old stem while the phloem stays a thin band.
• Cell types formed: xylem derivatives become vessel elements, tracheids, fibres and axial parenchyma. Phloem derivatives become sieve elements with companion cells, phloem parenchyma and phloem fibres (sclereids in older phloem).
• Division before maturation: a phloem mother cell divides unequally and lengthwise, giving a sieve-tube element and one or more companion cells from the same parent. Xylem derivatives mostly enlarge and mature directly, with no such sister-cell pairing.
• Growth in size: vessel derivatives expand greatly in diameter before the wall hardens. Sieve elements enlarge much less.
• Wall: xylem cells lay down a thick, lignified secondary wall with pits, patterned by cortical microtubules. Sieve elements keep a thin, unlignified wall, sometimes thickened as a "nacreous" layer.
• Fate of the protoplast: xylem conducting cells undergo programmed cell death, so the protoplast is removed and a dead, hollow tube remains. A sieve element loses its nucleus, vacuole membrane and most organelles, but it stays alive with its plasma membrane and some ER, plastids and mitochondria. Its companion cell sustains it.
• Later fate: older secondary xylem stays in place and in many trees becomes heartwood. Secondary phloem functions for a short time (often one season), then is crushed as new phloem is added, and much of it is shed with the bark.
• Control: auxin moves through the cambial zone and promotes xylem differentiation, and HD-ZIP III transcription factors favour xylem identity. A small peptide, TDIF (CLE41/44), made in the phloem, binds the PXY receptor in the cambium. This keeps the cambial cells dividing and holds back their differentiation into xylem. Phloem identity needs factors such as APL (ALTERED PHLOEM DEVELOPMENT).
• Seasonal pattern: in temperate trees the xylem forms annual rings (earlywood and latewood) and may be ring-porous or diffuse-porous. Phloem shows no comparable lasting rings.

How a vessel element differs from a sieve element

• Living state: a vessel element is dead at maturity, with no protoplast. A sieve element is living but enucleate.
• End walls: a vessel element has perforation plates (simple or scalariform) that are true openings, so the cells join into a continuous tube. A sieve element has sieve plates crossed by pores lined with callose, through which the protoplasts of neighbouring cells connect.
• Side walls: a vessel element has a thick, lignified secondary wall with bordered pits. A sieve element has a thin, primary, unlignified wall with sieve areas.
• Contents: a vessel element is empty, holding water under tension. A sieve element contains P-protein (in dicots), a parietal layer of cytoplasm, and ER.
• Associated cell: a vessel element has none tied to it developmentally. A sieve element has a companion cell, its sister cell, connected by many branched plasmodesmata.
• Function: a vessel element carries water and minerals upward. A sieve element carries sugars in either direction by pressure flow.
• Sealing on injury: a vessel is sealed by gums and tyloses. A sieve element is sealed quickly by P-protein and by callose deposited on the sieve plate.

(c) Variability in tissue-culture regenerants and its use in crop improvement

Plants regenerated from callus, cell suspension or protoplast culture are often not identical to the parent. Larkin and Scowcroft (1981) named this variation somaclonal variation. It is highest when there is a long callus phase or a disorganised (adventitious) route to regeneration.

Causes

1. Variation already in the explant: somatic cells of the donor may differ in ploidy (endopolyploidy, polysomaty) or carry somatic mutations, or the plant may be a chimera. Culture separates and fixes these differences.
2. Changes in chromosome number and structure: aneuploidy, polyploidy, deletions, duplications and translocations. Breakage often occurs in late-replicating heterochromatin.
3. Gene-level changes: point mutations, and changes in the copy number of repeated sequences such as rDNA.
4. Transposable elements: culture activates transposons and retrotransposons (for example Tnt1 and Tto1 in tobacco, and Tos17 in rice), which then insert into genes.
5. Epigenetic changes: altered DNA methylation and chromatin state. These may be stable, or they may revert; the mantled fruit abnormality in oil-palm clones comes from hypomethylation of the Karma retrotransposon.
6. Culture conditions: high doses of auxins such as 2,4-D, long culture periods, many subcultures, the genotype, and oxidative stress all raise the rate of variation.

Uses in crop improvement

Somaclonal variation, especially with in vitro selection (adding a pathogen toxin, salt, a herbicide or aluminium to the medium), gives new variants without crossing or transgenes. It is most useful in vegetatively propagated crops and in crops with a narrow genetic base.

Disease resistance:

• Sugarcane: somaclones resistant to Fiji disease, downy mildew and eyespot were obtained from susceptible cultivars in the 1970s (Heinz and co-workers in Hawaii; Krishnamurthi in Fiji).
• Banana: the Taiwan Banana Research Institute selected the Cavendish somaclone GCTCV-218 ('Formosana'), which tolerates Fusarium wilt Tropical Race 4.
• Maize: selection on the Helminthosporium (southern corn leaf blight) T-toxin gave toxin-resistant T-cytoplasm plants (Gengenbach et al., 1977).

Agronomic and quality traits:

• Potato: Shepard's protoclones of 'Russet Burbank' (1980) differed in tuber shape, maturity and blight response.
• Tomato: DNA Plant Technology's somaclone DNAP-9 has higher solids for processing.

Indian examples:

• Mustard: Pusa Jai Kisan (Brassica juncea), a somaclone of cv. Varuna released by IARI/NRCPB, has bolder seeds and higher yield.
• Java citronella: CSIR-CIMAP's Bio-13 (Cymbopogon winterianus) is reported to give more oil.
• Stress tolerance: salt-tolerant and aluminium-tolerant cell lines and regenerants have been selected in rice, tobacco and other crops.

Limitations. Many variants are undesirable (dwarfing, sterility, off-types). This is a serious problem in micropropagation, where uniform clones are wanted, such as the off-types in Cavendish banana. Some changes are epigenetic and fade in later generations, and the variation is random rather than targeted. Every variant therefore needs to be checked for stability over several seasons and locations before it is released.