Plant

Plants are eukaryotes. A typical photosynthetic leaf cell has a cell nucleus, mitochondria, chloroplasts, and a cell wall outside its cell membrane. A root cell need not have chloroplasts; the plant's parts specialize for different functions. Plants perform cellular respiration as well as photosynthesis. See OpenStax Biology 2e, 4.3: plant cell organization.

A lateral meristem producing secondary xylem inward and secondary phloem outward.

A storage shoot with a short stem and fleshy leaves or leaf bases; it is anatomically distinct from a root.

Secondary xylem produced by the vascular cambium.

The inner, generally nonconducting portion of a woody stem, distinguished from the more recently formed sapwood.

Plant tissues external to the vascular cambium of a woody stem or root.

An angiosperm whose aromatic rhizome supplies the spice ginger.^[ref]

A plant persisting for multiple years; repeated reproductive episodes and vegetative renewal create different allocation requirements from those of annual crops.

A plant completing its life cycle within one growing year; this does not imply that all varieties have identical flowering requirements.

An orchid studied for chemical mimicry of its pollinator’s female sex pheromone.

Capacity to survive substantial drying and recover function after rehydration. It differs from avoiding water loss. Recovery of one physiological signal does not establish successful growth and reproduction.

An anchoring structure on relevant plant bodies. It may contribute to water or nutrient uptake, but is not anatomically identical to a root.

A land plant with the specialized conducting tissues xylem and phloem. An independent, usually conspicuous sporophyte supports transport and growth; the ecological requirements of the gametophyte still matter for completing reproduction.

A plant lineage reproducing through seeds, including gymnosperms and angiosperms. Reduction and retention of gametophytes and male delivery through pollen distinguish their reproductive ecology from a typical free-living fern gametophyte.

A member of a seed-plant lineage whose ovules are not enclosed in angiosperm carpels. Conifers contribute extensively to forest carbon pools, but the lineage includes different growth forms and reproductive arrangements.

A gymnosperm genus used in comparisons of reproductive regulatory genes.^[ref]

A member of a vascular-plant lineage generally reproducing through spores rather than seeds. Most familiar fern bodies are sporophytes; their gametophytes can have different environmental requirements. heterospory and other life-cycle differences prevent treating every fern as one identical model.

A cluster of sporangia on a fern sporophyte.

A member of the land-plant lineages comprising mosses, liverworts and hornworts. Their persistent gametophytes support attached sporophytes; physiological independence should not be inferred merely from a green sporophyte.

A flower is an angiosperm's reproductive structure. Stamens produce pollen; carpels enclose ovules. Petals and sepals surround these organs in a complete flower, but some flowers lack one or more groups, including either reproductive group.^[ref]

Read the drawing from outside inward, then trace two routes: where pollen is released, and where an ovule is enclosed. This reveals why catching pollen and forming a seed require different structures. A detached petal cannot substitute for a stigma simply because both belong to the same flower.

A small flower, especially one forming part of a dense inflorescence such as a flower head.

Temporal separation of male and female reproductive function. It can reduce self-fertilization without requiring separate male and female flowers.

Spatial separation of male and female reproductive organs that can reduce self-pollen transfer while retaining them within one flower.

The floral structures surrounding the reproductive organs, often differentiated into sepals and petals. Protection and pollinator attraction can be combined in a shared display.

A part of the perianth when its members are not differentiated into sepals and petals.

The petals of a flower, collectively.

The outer envelope of a flower, composed of sepals.

A flower containing both male and female reproductive organs, stamens and carpels. It differs from monoecy, in which male and female structures occur separately on the same individual.

The organization of symmetry in a flower. Whole-flower symmetry, individual organ shape and developmental identity are distinct characters; similar outlines can arise through different molecular mechanisms.

A floral arrangement with one principal symmetry plane. Differential deployment of dorsal regulators can contribute, but a shared appearance does not establish one universal developmental mechanism.

A floral arrangement with multiple planes of symmetry around the reproductive axis. Its developmental basis can differ among lineages, so a derived radial flower need not restore the ancestral organ identities.

A stamen is a flower's male reproductive organ, typically an anther supported by a stamen filament. The anther produces and releases pollen.^[ref]

The pollen-producing part of a stamen.

The stalk supporting an anther.

The stigma is the carpel's pollen-receiving region. Compatible pollen may form a pollen tube that grows toward an ovule; arrival alone does not establish fertilization.^[ref]

A useful diagnostic question is what was actually observed: pollen on a stigma, a growing pollen tube, or a new plant embryo? Each observation tests a different stage. A pollen tube germination assay isolates the middle process for direct viewing.

A female reproductive unit of a flower, comprising a stigma, a style and an ovary. A flower may have several carpels, including fused ones.^[ref]

The connection between the stigma and ovary through which a pollen tube can grow.

The carpel region enclosing one or more ovules.

The structure containing the angiosperm female gametophyte; a fertilized ovule can develop into a seed.

The gametophyte inside an angiosperm's ovule, containing an ovum and, in the common arrangement, a central biological cell with two polar cell nuclei.^[ref]

A flower organ surrounding the reproductive structures, often conspicuous.

An outer flower organ often protecting the unopened bud.

A seed packages a plant embryo, a seed food reserve and a protective seed coat. It is a living starting point for a new plant, not merely stored food. In a mature pea seed, the large cotyledons hold reserves; other seeds retain substantial endosperm. These are alternative arrangements, not successive germination stages.^[ref]

A useful reading exercise is to identify both the future plant and its initial food supply in each drawing. The large yellow area has the same role in both pictures, but it belongs to different plant tissues. Thus location and function alone do not establish tissue identity.

The capacity of a seed lot to germinate and establish under specified conditions, distinguished from viability alone.

The young plant inside a seed; its cotyledons and radicle are parts of the plant embryo.

An embryonic leaf; a cotyledon can store a seed food reserve or help transfer it.

The embryonic root; radicle protrusion commonly marks completion of germination.

The protective covering of a seed, formed from maternal plant tissues surrounding the developing plant embryo.

Stored material supporting early seedling growth, located in cotyledons, endosperm or other plant tissues depending on the plant.

A nutritive plant tissue distinct from the plant embryo; it may remain in the mature seed or be depleted during development.^[ref]

A young plant developing after germination. Early growth can use a seed food reserve before leaves support photosynthesis.^[ref]

Seed germination is renewed plant embryo activity and growth. Many germination assays score completion as radicle emergence, before seedling establishment. Seed imbibition precedes that endpoint; swelling alone is insufficient.^[ref]

Water, molecular oxygen and suitable temperature support germination; light sensitivity depends on the species and seed state. Neither illumination nor one particular temperature is universally required. Seed dormancy connects germination timing to ecology by delaying seedling establishment.^[ref]

The distinction matters when comparing propagation experiments: a treatment that increases radicle emergence need not improve later seedling survival. Define the endpoint before comparing treatments, then measure the later outcome separately.

Initial seed water uptake, permitting renewed metabolism. Hydration does not prove seed viability or imply the idealized hydraulic law for capillary imbibition.^[ref]

A living seed's restriction on germination under otherwise favorable conditions, distinct from insufficient water, unsuitable temperature or lost seed viability. One failed test cannot diagnose seed dormancy.^[ref]

The capacity of a living seed to produce a developing plant under suitable conditions. A seed with seed dormancy can retain seed viability. In an ideal counting exercise, if $g$ of $N$ seeds complete germination, at least $g$ were living at the start. The other $N-g$ are unresolved: a failed germination assay alone cannot separate dead seeds, seed dormancy and unsuitable conditions.

The 1952 experiment used Grand Rapids lettuce seeds on wetted blotters in covered dishes. After 16 hours in darkness, seven lots of 200 received successive alternating exposures: one minute of red light at $580$–$680\mathrm{nm}$, then four minutes above $700\mathrm{nm}$, with one lot removed after each exposure. Treated lots and a dark scientific control remained at $20{}^{\circ }\mathrm{C}$ for two days; germinated seeds were counted. Separate wavelength tests used a two-glass-prism spectrograph.^[ref]

Table 1 shows alternating promotion and suppression according to the final exposure. Red light could restore promotion after far-red light; suppression was incomplete. This reversibility supports a reversible sensing state rather than simple cumulative illumination. The paper did not isolate or identify the pigment; the response concerns this lettuce preparation and timing. Its readout was a two-day germination count, not subsequent seedling performance.^[ref]

The modern phytochrome description distinguishes forms $P_r$ and $P_{fr}$ that interconvert under red and far-red light. This provides a concrete example of signal transduction: light changes a sensing state that affects development. The response should be distinguished from photosynthesis, which supplies chemical resources.^[ref]

A specified test for germination, recording the endpoint, conditions and observation window. For a proposed red/far-red light test, use randomization to allocate one seed lot to darkness, red, red then far-red, and red then far-red then red. Match hydration, temperature, handling and elapsed time before counting; use sham waiting periods to equalize schedules. Use dish replication, retain the dark scientific control, and record radicle emergence using an observation procedure that does not itself provide an uncontrolled light treatment. This is a proposed design, not a claim about the 1952 paper's randomization or replication.

As an original hypothetical counting example, begin with $N=40$ seeds in one dish. Suppose 12 first meet the radicle endpoint by 24 hours, eight additional seeds by 48 hours, and four additional seeds by 72 hours. These invented event counts giveand cumulative sample proportions $\hat{G}(24)=0.30$, $\hat{G}(48)=0.50$ and $\hat{G}(72)=0.60$. The 48-hour increment is $8/40=0.20$, not $0.50$; the latter includes earlier events. Counting the same emerged radicle again at each inspection would inflate the total. These numbers illustrate bookkeeping, not biological rates or treatment effects.

With a fixed denominator and irreversible classification of the first endpoint event, the set counted at an earlier inspection is a subset of the set counted later. Hence $0\le \hat{G}(t)\le 1$ and $\hat{G}(t)$ cannot decrease. This short proof applies to cumulative germination counts even if a later seedling dies. A count of currently surviving seedlings has a different definition and can decrease.

For treatment comparisons, the dish may be the experimental unit: seeds in the same dish share conditions. Forty seeds in one dish do not supply forty independent dish replicates. Report the sample size, replication, endpoint time and denominator; a sample proportion by a deadline measures this assay's outcome, not an unconditional fraction with seed viability.

A plant used in the lettuce red and far-red germination experiment.

A plant organ; the embryonic root is the radicle.

A root arising from a non-root organ, such as a plant stem.

A plant organ; a cotyledon is an embryonic leaf.

A grouping of biological cells in a plant with related functions. In a seed, plant embryo tissues and endosperm have distinct developmental identities.

A region maintaining cells that support continued plant growth and organ production. Floral reproductive development coordinates organ identity with changes in the activity and termination of its meristem.

A surface barrier that limits water exchange with the environment. Its development helps regulate drying, but varies between gametophytes, sporophytes and plant organs.

A pore with associated guard cells in the plant surface. Distribution and function differ among life-cycle stages and lineages; a liverwort air pore is not an equivalent regulated structure.

Reduction of stomatal aperture through changes in guard cell mechanics and turgor pressure. In ABA responses, regulated solute efflux promotes water loss from guard cells.

Conducting tissue transporting organic compounds and other materials between source and sink regions of a vascular plant.

Explanation of bulk assimilate transport from source to sink through hydrostatic pressure differences associated with solute loading and unloading.

Conducting tissue carrying water and dissolved materials through a vascular plant. Its anatomy and vulnerability to water stress affect plant stature, growth and survival.

An elongated water-conducting cell in xylem. Its transport and support roles help explain the hydraulic organization of many gymnosperms.

A plant that produces flowers and encloses its ovules within an ovary.

Dandelion; the 1867 medicinal root article uses the historical name Taraxacum dens leonis.

The botanical source of croton oil.

The source of the seeds from which cocoa butter is expressed.

The source of the medicinal seed called Calabar bean.

The source of the sliced or rasped heartwood called Pterocarpi lignum.

The fleshy fruiting structure of a rose, distinct from its petals.

The source of the fresh and dried unexpanded red-rose petals specified in the 1867 standard.

The botanical source of fresh elder flowers, Sambuci flores in the 1867 standard.

An angiosperm with flowers arranged in an umbel.^[ref]