Anatomy of Flowering Plants

Story: Imagine building site. Apical meristem at tip of root and shoot — does primary growth length like building getting taller. Root tip apical covered by root cap like helmet. Shoot tip protected by leaf primordia. Intercalary at base of internode in grasses — that is why grass regrows after you cut lawn, workers sitting at base push up. Lateral on sides — vascular cambium and cork cambium — does secondary growth thickness like tree trunk increasing girth every year, like you adding layers to wall. Primary meristem from promeristem direct, secondary from permanent tissues that become meristem again dedifferentiation like retired worker returning. Once you see tips + sides, you know where growth happens.

Parenchyma = thin cellulose wall, isodiametric living with intercellular spaces like cotton balls, stores food, does photosynthesis chlorenchyma, floats aerenchyma in aquatic lotus with air cavities like swimming tube. Collenchyma = thick at corners with pectin hemicellulose like corner pillars extra cement, living, below epidermis in dicot stem gives flexibility — you can bend stem without breaking like collar. Sclerenchyma = thick lignified dead like stone, no protoplasm, 2 types: fibres long thread-like jute hemp you make rope, sclereids gritty stone cells in pear, guava, tea leaves you feel grit while chewing. One soft cotton, one flexible collar, one stone hard — all three bricks.

Xylem = water pipeline from root to leaf, one-way up. 4 elements: Tracheids elongated tapering with bordered pits like straw with holes, main in gymnosperms. Vessels cylindrical tube with perforation plates like water pipes joined end to end better conduction in angiosperms. Xylem parenchyma living storage. Xylem fibres dead support like steel rods. Protoxylem first small, Metaxylem later big. In root exarch protoxylem outside centripetal inside, in stem endarch protoxylem inside centrifugal outside — remember exarch = root EXits outside, endarch = stem ENters inside.

Phloem = food pipeline leaf to all, two-way. 4 elements: Sieve tube elements enucleate with sieve plates pores like sieve, Companion cells dense cytoplasm with nucleus controls sieve tube via plasmodesmata like manager controlling worker, Phloem parenchyma, Phloem fibres bast fibres only dead element you use for jute, flax, hemp ropes. Protophloem first, metaphloem later. Sieve tube has P-protein callose winter blocks.

Epidermal system = outermost skin single parenchyma with cuticle wax waterproof layer like raincoat. Stomata = 2 guard cells kidney shaped dicot, dumbbell monocot + subsidiary cells around, open close by K+ water turgor like gate guards opening closing gate for air. Trichomes = epidermal hairs unicellular multicellular branched for protection like thorns, root hairs absorption.

Ground = all except epidermal vascular = cortex, pericycle, pith, medullary rays parenchyma mostly like filling material.

Vascular = xylem + phloem. Radial = xylem phloem alternate on different radii like alternate seats in root. Conjoint = same radius stem leaf. Collateral open with cambium between xylem phloem dicot so secondary growth possible like open shop can add stock, closed without cambium monocot like closed shop cannot add. Bicollateral phloem both sides xylem middle in Cucurbita.

Both have: Epiblema outer with root hairs like absorptive hairs, Cortex parenchyma many layers storage, Endodermis single with Casparian strips waxy suberin like waterproof band prevents leakage, Pericycle gives lateral roots and cork cambium like mother of branches, Vascular radial exarch, Conjunctive tissue parenchyma between xylem phloem, Pith centre.

Dicot root: Exarch 2-4 protoxylem called tetrarch (4) diarch (2) triarch (3), Pith small or absent like no centre, Conjunctive parenchyma, Secondary growth happens — you get thick roots of trees.

Monocot root: Polyarch many protoxylem >6 like many spokes in cycle wheel, Pith large well developed like big centre hall, No secondary growth — that is why no thick tree roots in monocot, only fibrous shallow roots you can pull easily. Remember: Dicot small pith poly? No, mono large pith polyarch.

Dicot stem: Epidermis cuticle + trichomes hairs, Hypodermis collenchyma below epidermis like collar strength, Cortex parenchyma, Endodermis starch sheath with starch grains, Pericycle semilunar sclerenchyma patches above each phloem like caps, Vascular open conjoint collateral arranged in ring Eustele like people sitting in circle holding hands, Medullary rays parenchyma between bundles like gaps between people, Pith large central parenchyma like hall centre. Secondary growth yes.

Monocot stem: Epidermis cuticle, Hypodermis sclerenchyma not collenchyma — stone hard, Ground tissue no differentiation no cortex pericycle pith all same parenchyma like no departments all same filling, Vascular scattered atactostele closed conjoint collateral no cambium scattered like people randomly sitting in ground, each bundle with sclerenchyma sheath like cap, lysigenous cavity water cavity in phloem side like hole, No secondary growth — that is why bamboo grass never becomes thick tree.

Dicot leaf dorsiventral = upper lower different like two-faced. Upper epidermis thick cuticle wax, Upper mesophyll palisade 2 layers elongated tightly packed with chloroplasts like pillars facing sun for max light, Lower mesophyll spongy with air spaces like sponge for gaseous exchange, Stomata more on lower hypostomatic to save water, Vascular bundles with bundle sheath, Midrib with collenchyma upper lower for support, Xylem above phloem below.

Monocot leaf isobilateral same both sides like both faces equal. No palisade spongy differentiation, all mesophyll similar isodiametric. Stomata equal both sides amphistomatic. Special motor cells bulliform large empty bubble-like on upper epidermis help leaf rolling during drought to reduce transpiration like you roll paper to save — when dry, bulliform loses water and leaf rolls, when wet opens. Parallel venation. Remember bulliform = bulging motor fan.

In dicot stem: Fascicular cambium inside bundles already present + Interfascicular cambium from medullary rays dedifferentiation (parenchyma becomes meristem again) join to form continuous cambium ring like bangle. Ring cuts off secondary xylem inside secondary phloem outside like inside wood outside food. Spring wood early wood light large vessels more water in spring, Autumn wood late wood dark small dense less water in autumn. Annual rings = one spring + one autumn = 1 year, count for age dendrochronology like counting bangles.

Then cork cambium phellogen from cortex/pericycle forms phellem cork dead suberized outside like bark outer + phelloderm living inside = Periderm. Bark = all outside vascular cambium (periderm + secondary phloem) like everything outside ring. Lenticels lens-shaped pores in bark for gaseous exchange like windows in bark.

Wood: Heartwood central dark dead filled with tannins resins oils gums non-conducting durable like old furniture, Sapwood outer light living conducts water like new wood. Heartwood does not conduct but gives strength, more durable, you make furniture from heartwood. Sapwood is new, light, conducts.