(a) Mention the diagnostic features of family Apiaceae and Solanaceae. Write the botanical names and uses of five members from…

(a) Diagnostic features of Apiaceae and Solanaceae, with names and uses of five members of each (20 marks)

Diagnostic features (10 marks).

Apiaceae (Umbelliferae):

• Aromatic herbs with hollow (fistular), furrowed stems and oil ducts (schizogenous) containing essential oils.
• Leaves alternate, pinnately compound or much dissected, with a sheathing base.
• Inflorescence a compound umbel, with an involucre and involucels.
• Flowers small, bisexual, epigynous and pentamerous, with minute sepals and five free petals, five stamens and a nectar-secreting stylopodium.
• Ovary inferior, of two fused carpels, bilocular, with one pendulous ovule in each; fruit a cremocarp that splits into two one-seeded mericarps hanging from a carpophore; formula ⊕ ⚥ K(5) or 0 C5 A5 G̅(2).

Solanaceae:

• Herbs, shrubs or small trees; leaves simple, alternate and exstipulate; vascular bundles bicollateral, with internal phloem.
• Inflorescence cymose, often extra-axillary or leaf-opposed.
• Flowers actinomorphic, bisexual and hypogynous; calyx of five united persistent sepals, corolla of five united petals (rotate or campanulate), five epipetalous stamens alternating with the petals, anthers often opening by pores.
• Ovary superior, bicarpellary, bilocular with an obliquely placed septum and swollen axile placentae; fruit a berry or capsule; formula ⊕ ⚥ K(5) C(5) A5 G(2). Alkaloids are characteristic.

Botanical names and uses (10 marks).

Apiaceae:

• Coriandrum sativum (coriander): leaves and fruits as spice and garnish.
• Cuminum cyminum (cumin): seeds as spice, carminative.
• Foeniculum vulgare (fennel): fruits as spice and mouth-freshener; carminative.
• Daucus carota (carrot): edible root, rich in carotene.
• Trachyspermum ammi (ajwain): fruits as spice, and thymol for digestive and antiseptic use.

Solanaceae:

• Solanum tuberosum (potato): edible starchy tuber.
• Solanum lycopersicum (tomato): fruit as vegetable, rich in lycopene and vitamin C.
• Solanum melongena (brinjal): fruit as vegetable.
• Capsicum annuum (chilli): fruit as spice, source of capsaicin.
• Withania somnifera (ashwagandha): root used as a tonic in Ayurveda; also Nicotiana tabacum (tobacco) for nicotine and Atropa belladonna for atropine.

(b) Botanical gardens as outdoor laboratories for botanists (15 marks)

A botanical garden is a living collection of plants, labelled and arranged for study, and it serves as a laboratory in the open in these ways:

• Taxonomy: living plants named and documented are reference material beside the herbarium, letting botanists study variation, flowering and fruiting through the year, and compare related taxa side by side. Seeds are exchanged through Index Seminum.
• Conservation: ex situ conservation of endangered and endemic species, with seed banks, propagation and reintroduction, as at Kew and in India at the National Botanical Research Institute, Lucknow.
• Introduction and acclimatisation: economic plants such as cinchona, tea and rubber were first tried in gardens; the Indian Botanic Garden at Howrah, founded in 1787, played a part in this.
• Experimental research: plant physiology, anatomy, cytology, genetics, breeding and ecology, including phenology and the effects of climate change; DNA barcoding needs authenticated material.
• Economic and medicinal botany: gardens grow herbs, spices, timber and drug plants for study and for bioprospecting.
• Education and public awareness: teaching, field practicals, identification and training for students, and plant-science education for the public.
• Horticulture: development and display of ornamentals, and hybrid and cultivar trials.

Hence a botanical garden gives botanists what a field station or a laboratory gives, a supply of authenticated, living material under known conditions, to study and to protect plants.

(c) Components of xylem and its role in survival and growth of plants (15 marks)

Xylem is the complex tissue that conducts water and minerals, and it has four kinds of elements (12 marks):

• Tracheids: long, tapering, dead cells with lignified walls and bordered pits, with no perforation. They conduct water through the pits and give strength. They are the main water-conducting cells of pteridophytes and gymnosperms.
• Vessels (tracheae): tubes of dead vessel elements placed end to end, with perforated end walls and wide lumens, so they carry water rapidly. They are typical of angiosperms, with annular, spiral, scalariform, reticulate or pitted thickening.
• Xylem fibres: elongated, thick-walled sclerenchyma cells (libriform fibres and fibre-tracheids), which give mechanical strength.
• Xylem parenchyma: living cells, in axial strands and in rays, that store starch and fats, transport water and food radially, and form tyloses that block old vessels.

Protoxylem, first formed with annular and spiral thickening, and metaxylem, with pitted thickening, form the primary xylem, and secondary xylem is the wood, in which sapwood conducts and heartwood only supports.

Role (3 marks). Xylem carries water and minerals from roots to leaves, by transpiration pull and cohesion, so that photosynthesis and growth continue; it gives mechanical support, allowing tall growth on land; and it stores food. Secondary xylem increases stem girth and gives timber.