🌿 Botany: Historical Timeline & Scientific Milestones

Demonstrated experimentally in 'De Sexu Plantarum Epistola' that removing male anthers from monoecious (castor bean) or dioecious (mulberry) plants prevents female ovaries from setting viable seed.

Measured root pressure and transpiration rates quantitatively using manometers, demonstrating that plants transpire enormous quantities of water and take in nourishment from the atmosphere through leaves.

Established the universal binomial nomenclature system (Genus + specific epithet) for classifying 7,300 plant species into 24 classes based on the number and arrangement of floral stamens and pistils.

Demonstrated that submerged aquatic plants (Elodea) produce bubbles of dephlogisticated air (oxygen) only when exposed to bright sunlight, and only from their green stems and leaves, purifying fouled air.

Conducted precise gravimetric gas-exchange experiments, demonstrating that the gain in plant dry weight exceeds the weight of absorbed carbon dioxide, proving water is consumed as an essential reactant.

Demonstrated the universal developmental homology linking bryophytes, pteridophytes, gymnosperms, and angiosperms through regular alternation between a haploid gametophyte and diploid sporophyte generation.

Cultivated plants to complete maturity in defined aqueous mineral nutrient solutions without soil, identifying the essential macro- and micronutrients required for plant life.

Demonstrated in 'The Power of Movement in Plants' that canary grass coleoptiles bend toward unilateral light, but capping the tip with an opaque foil cap abolishes bending, deducing an influence transmits downward.

Split white light through a glass prism onto a filamentous green alga (Cladophora) and added aerotactic bacteria (Bacterium termo), which clustered densely around the blue (400-450 nm) and red (650-680 nm) light zones.

Proposed that water ascent in tall trees (>100 meters) is driven entirely by solar-evaporative transpiration pull transmitted through continuous xylem conduits under massive negative hydrostatic pressure (tension).

Discovered in Lilium martagon and Fritillaria that both sperm nuclei from the pollen tube participate in syngamy: one fertilizes the haploid egg to form the diploid zygote, while the other fuses with two polar nuclei to form the triploid endosperm.

Discovered that a giant mutant tobacco cultivar (Maryland Mammoth) failed to flower in summer but flowered luxuriantly in winter greenhouses, proving flowering is governed by the relative duration of day and night (photoperiod).

Investigated the 'bakanae' (foolish seedling) disease of rice characterized by excessive, spindly stem elongation, demonstrating that sterile filtered culture extracts of the fungus Gibberella fujikuroi induced identical hyper-elongation in healthy rice seedlings.

Excised oat (Avena sativa) coleoptile tips, placed them onto agar blocks to allow diffusible hormone to collect, and placed the agar block asymmetrically onto decapitated stumps, producing curvature directly proportional to hormone quantity.

Proposed that phloem sap flows en masse through sieve tubes driven by an osmotic hydrostatic pressure gradient between photosynthetic sources (high turgor) and non-photosynthetic sinks (low turgor).

Illuminated isolated chickweed chloroplasts in the presence of an artificial electron acceptor (potassium ferricyanide) in the complete absence of CO2, observing vigorous oxygen evolution.

Isolated an adenine derivative (6-furfurylaminopurine, 'kinetin') from autoclaved herring sperm DNA that dramatically stimulated cell division in cultured tobacco pith parenchyma explants.

Fed green alga Chlorella with 14CO2 for fractions of a second, killed cells in boiling ethanol, and used 2D paper chromatography to identify the first stable carbon fixation product: 3-phosphoglycerate (3-PGA) (1961 Nobel Prize).

Discovered that red light (660 nm) stimulates seed germination and inhibits flowering in short-day plants, while immediate far-red light (730 nm) cancels the effect, isolating the photoreversible chromoprotein 'phytochrome'.

Addicott isolated an abscission-accelerating substance from cotton bolls (Abscisin II); Wareing isolated a bud dormancy-inducing compound from sycamore leaves (Dormin); confirmed to be the identical sesquiterpenoid: Abscisic Acid (ABA).

Demonstrated that sugarcane leaves pulse-labeled with 14CO2 fix carbon initially into 4-carbon dicarboxylic acids (oxaloacetate, malate, aspartate) rather than 3-PGA, mapping the Hatch-Slack (C4) pathway.

Elucidated how desert succulents (Cactaceae, Crassulaceae, pineapple) adapt to arid environments by opening stomata only at night to fix CO2 into malic acid stored in giant central vacuoles.

Promoted the tiny cruciferous weed thale cress (Arabidopsis thaliana) as the universal experimental model for plant molecular genetics due to its small genome (~125 Mb), short 6-week generation time, and self-pollinating nature.

Formulated the combinatorial ABC model of floral organ specification based on homeotic floral mutants in Antirrhinum (snapdragon) and Arabidopsis.

Cloned the non-phototropic hypocotyl 1 (nph1) mutant in Arabidopsis, identifying the flavoprotein kinase 'phototropin' (phot1 and phot2) as the true blue-light receptor directing phototropic curvature.

Published the complete 115.4-megabase euchromatic sequence of Arabidopsis thaliana, representing the first complete genome sequence of a flowering plant, encoding ~25,500 genes.

Solved the 70-year-old enigma of Mikhail Chailakhyan's hypothetical flowering hormone 'florigen', proving that the FLOWERING LOCUS T (FT) protein itself, rather than its mRNA, is the systemic mobile signal.

Sequenced transcriptomes from 1,124 land plant and streptophyte algal species spanning over one billion years of viridiplantae evolutionary history, resolving deep contentious branches.