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Equisetum arvense. (a) Sterile shoot. (b) Fertile shoot growing from an underground rootstock. (c) Cone. (d) Two views of shield-shaped sporangiophores. (e) Spores, greatly enlarged. As spore dries, elaters expand. (After E. W. Sinnott and K. S.…

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from article Equisetales

Equisetum gametophyte. (a) Small gametophyte, showing antheridia only. (b) Male gametes. (c) Larger gametophyte; branching lobes have archegonia at bases. (After E. W. Sinnott and K. S. Wilson, Botany: Principles and Problems, 6th ed., McGraw-Hill,…

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from article Equisetales

Sporophytes. (a) Equisetum gametophyte with sporophytes. (b, c, d) The young sporophytes of Equisetum hiemale. (After G. M. Smith, Cryptogamic Botany, vol. 2, 2d ed., McGraw-Hill, 1955)

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from article Animal testing

Mice are the most commonly used vertebrate species in animal testing and research. (Credit: Dolores Bonaparte)

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from article Animal testing

The use of animals in biomedical research remains essential, but the handling of these sentient beings must be done humanely to minimize and prevent animal harm. (Credit: U.S. Department of Agriculture)

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from article Pathotoxin

Oat seedling resistant to Victoria blight obtained by screening a susceptible population with the pathotoxin victorin, a product of the pathogen Helminthosporium victoriae.

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from article Pathotoxin

Separation of corn seedlings resistant (N) and susceptible (T) to southern corn leaf blight by treatment with a pathotoxin produced by Helminthosporium maydis race T.

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from article Pathotoxin

Chemical structures of four pathotoxins. (a) Fusicoccin. (b) Tentoxin. (c) AM-toxin. (d) HMT-toxin.

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from article Tree ferns

Cyathea cooperi (Australian tree fern), a common member of the family Cyatheaceae. (Photo by Forest and Kim Starr)

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from article Tree ferns

Arrangement of leaves of Cyathea cooperi (Australian tree fern). (Photo by Bryan Harry, Haleakalā National Park, National Park Service, Maui, Hawaii)

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from article Circadian clock (plants)

Three-module circadian clock system.

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from article Circadian clock (plants)

Model of the Arabidopsis circadian clock, showing light input (bold arrow), the central oscillator (large box) and output/response (tinted arrows). Light signals synchronize the clock via the cryptochromes (cry) and phytochromes (phy). These are…

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from article Poplar

Quaking aspen (Populus tremuloides). (Photo courtesy of North Dakota State Soil Conservation Committee, USDA–NRCS PLANTS Database)

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from article Poplar

Common poplar species. (a) Quaking aspen (P. tremuloides); leaf scar with an axial bud, leaf, and twig. (b) Bigtooth aspen (P. grandidentata); leaf, terminal bud, and twig. (c) Cottonwood poplar (P. deltoides); leaf, leaf scar, terminal bud, and…

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from article Gibberellins

ent-Gibberellane carbon skeleton showing the carbon numbering system and ring designations.

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from article Gibberellins

The GA-biosynthetic pathway in higher plants via 2-methylerythritol-4-phosphate (MEP). The biologically active end products of the pathway are GA1, GA3, and GA4. The general diterpene precursor trans-geranylgeranyldiphosphate (GGPP) is formed in…

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from article Gibberellins

Mechanisms for GA inactivation. C19-GAs and C20-GAs may be oxidized on C-2 by different classes of GA 2-oxidases (GA2ox). In rice, the enzyme ELONGATED UPPER INTERNODE (EUI) oxidizes the 16,17-double bond of non–13-hydroxylated GAs, such as GA4, to…

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from article Gibberellins

DELLA protein showing conserved domains, and a model for DELLA degradation via the SCF E3 ubiquitin ligase, which consists of a DELLA-specific F-box, Skp1, Cullin1 (CUL), and Rbx1 subunits. Binding of the GID1-GA complex to DELLAs promotes…

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from article Gibberellins

Model for GA-induced production of α-amylase in the aleurone of germinating cereal grains. GAs produced in the scutellum diffuse to the aleurone cells, where they stimulate transcription, processing, and secretion of α-amylase and other hydrolytic…

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from article Chlorophyceae

Chlorococcales. (a) Chlorococcum (Chlorococcaceae), vegetative cell; (b) cell with zoospores; (c) zoospores; (d) Hydrodictyon (Hydrodictyaceae), portion of coenobium; (e) portion enlarged; (f) Dictyosphaerium (Dictyosphaeriaceae), colony in…

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from article Chlorophyceae

Filamentous green algae with chlorophycean ultrastructure. (a) Microspora (Microsporales), showing H-shaped wall segments; (b) Sphaeroplea (Sphaeropleales); (c) Chaetophora (Chaetophorales), heterotrichous thallus (erect and prostrate systems).

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from article Chlorophyceae

Ulothrix (Ulotrichales).

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from article Osage orange

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from article Bryopsidales

Anatomical structures of selected members of Bryopsidales. (a) Dichotomosiphon, filament with oogonia and antheridia. (b) Ostreobium, filaments. (c) Caulerpa, section of filament showing trabeculae. (d) Codium, group of utricles with gametangia and…

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from article Bryopsidales

Representative members of Bryopsidales. (a) Bryopsis; (b) Caulerpa; (c) Penicillus; (d) Halimeda; (e) Codium.

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from article Magnolia

Flowers and leaves of the southern magnolia (Magnolia grandiflora). (Photo courtesy of Forest and Kim Starr)

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from article Hackberry

Hackberry (Celtis occidentalis). (Credit: North Dakota State Soil Conservation Committee, USDA–NRCS PLANTS Database)

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from article Plant vulnerability to climate change

Subarctic tundra and vegetation of the Denali National Park and Preserve in Alaska. As a result of climate change and the resultant poleward and upward shift of plant ranges, plants and their ecosystems may become particularly vulnerable. (Credit:…

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from article Plant vulnerability to climate change

Blue grama (Bouteloua gracilis) growing in Montana. As a result of warming temperatures, this type of grass could face decreased productivity, allowing forbs to increase and making the ecosystem less tolerant of drought and grazing. (Credit: Matt…

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from article Plant vulnerability to climate change

Modeled distribution of suitable climate space in Europe for stiff sedge (Carex bigelowii), which is an Arctic-Alpine plant: (a) during the period 1961–1990 (green color = suitable climate space during the 1961–1990 period); (b) climate model…

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from article Plant vulnerability to climate change

The endangered western prairie fringed orchid (Platanthera praeclara) is declining across much of its range in North America. (Credit: U.S. Fish and Wildlife Service)

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from article Plant juvenility

The basic miRNA, siRNA, and ta-siRNA pathways in plants. The enzymes that carry out the different steps are written to the right of the downward arrows. The miRNA pathway schematic shows processing of the hairpin into an miRNA:miRNA* duplex by the…

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from article Plant juvenility

The developmental expression patterns of genes that regulate vegetative phase change. This graph is meant to show only the changes in expression for each gene during development rather than actual expression levels or relative levels between genes.

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from article Rosemary

Leaves of rosemary (Rosmarinus officinalis). (Photograph courtesy of Forest and Kim Starr)

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from article Squash

Zucchini (Cucurbita pepo), a type of summer squash, with flowers. (Credit: Howard F. Schwartz, Colorado State University/www.Bugwood.org)

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from article Squash

Crookneck squash (Cucurbita moschata). (Credit: Howard F. Schwartz, Colorado State University/www.Bugwood.org)

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from article Squash

Delicata squash (Cucurbita pepo), a variety of winter squash. (Credit: Shaun Case)

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from article Squash

Leaves of Cucurbita pepo infected by a squash mosaic virus. (Credit: William M. Brown, Jr./www.Bugwood.org)

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from article Llama

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from article Dormancy

Viviparous seeds of maize (Zea mays) germinating on the cob because of a mutation (vp14) preventing abscisic acid synthesis. (From S. H. Schwartz and J. A. D. Zeevaart, Abscisic acid biosynthesis and metabolism, pp. 137–155, in P. J. Davies, ed.,…

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from article Phaeophyceae

Embryonic sporophyte of Desmarestia anceps, showing trichothallic growth resulting in an embryonic stipe and several pairs of embryonic branches.

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from article Cashew

Cashew (Anacardium occidentale). The cashew nut is contained in a hard shell at the bottom of the fruit (cashew apple). (Photo courtesy of Laura Lartigue, U.S. Agency for International Development, Guinea)

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from article Biological insect control

The emerald ash borer (Agrilus planipennis) is an invasive pest insect that damages ash tree species in North America and Europe. Researchers are searching for natural enemies against the borer in its native range (Asia) to use as biological control…

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from article Winged bean

Winged bean (Psophocarpus tetragonolobus). (Photo by Forest and Kim Starr)

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from article Garlic

Bulbs of garlic (Allium sativum). (Photograph by Forest and Kim Starr)

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from article Coriander

Coriander seeds (Coriandrum sativum). (Photograph courtesy of Steve Hurst, USDA–NRCS PLANTS Database)

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from article Strawberry

June-bearing strawberries (Fragaria × ananassa), which are produced in early summer. (Photo courtesy of Kimberly Lewers, Agricultural Research Service, United States Department of Agriculture)

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from article Strawberry

Botrytis cinerea fungal sporulation on a ripe strawberry. (Photo courtesy of Scott Bauer, Agricultural Research Service, United States Department of Agriculture)

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from article Scrophulariales

Flowers of the common snapdragon (Antirrhinum majus), a typical member of the family Scrophulariaceae in the order Scrophulariales (Lamiales). (Photo by Ondřej Zicha, BioLib, Czech Republic)

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from article Venus' flytrap

Dionaea muscipula (the Venus' flytrap) growing in a South Carolina nature preserve. Winged petioles and traps in various stages of the capture cycle are visible. The plant is surrounded by Sphagnum moss, which is a frequent community associate.…

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from article Venus' flytrap

Stages in the capture and digestion of a fly by the Venus' flytrap. A prey item is attracted to the trap margins by nectar (a). When a trigger hair on the inside leaf surface is twice stimulated (b), the trap closes rapidly (c). Complete closure is…

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from article Oats

Oats (genus Avena). (Photo by Jan Samanek, State Phytosanitary Administration, Czech Republic)

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from article Oats

Oat panicles with many branches and spikelets. (Photo by Jan Samanek, State Phytosanitary Administration, Czech Republic)

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from article Oats

Oat florets. Scale bar = 1 cm (0.4 in.). (Photo by Steve Hurst, USDA–Natural Resources Conservation Service PLANTS Database)

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from article Oats

Crown rust on oat leaves. This devastating disease is caused by Puccinia coronata. (Photo courtesy of the USDA Agricultural Research Service)

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from article Oats

Stem rust infection (caused by Puccinia graminis) on oat stems. (Photo by Howard F. Schwartz, Colorado State University)

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from article Cell plastids

Light microscope view of part of Hypochaeris radicata leaf, showing chloroplasts sectioned in a variety of planes and displaying internal grana.

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from article Cell plastids

Three-dimensional model of grana with intergranal connections. (After W. Wehrmeyer, Planta, 63:13–30, 1964)

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from article Cell plastids

Electron microscope view of two oat leaf chloroplasts, one showing successive layers of grana in side view, and the other showing grana in face view (disk shape of constituent thylakoid lobes are seen).

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from article Cell plastids

Part of oat leaf chloroplast at higher magnification. Grana are seen in side view, revealing profiles of membranes. Thylakoids that interconnect grana are shown, with components of stroma, or ground substance, in which thylakoids lie. The dense…

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from article Cell plastids

Proplastid in cell of broad bean root tip. Double membranous envelope is shown and rudimentary nature of internal membrane system is obvious.

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from article Agronomy

Relationship of agronomy to basic sciences, related fields, and practical farming methods.

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from article Forest ecosystem

Forest in Moran State Park on Orcas Island, Washington. (Credit: Chris Willig)

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from article Forest ecosystem

Forest fire in No Name Creek area of Colorado. (Credit: Andrea Booher/FEMA)

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from article Forest ecosystem

Puma and cub in forest. (Credit: Grant Faint/Stockbyte/Getty Images)

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from article Forest ecosystem

Conceptual model of elemental cycling in a terrestial ecosystem, emphasizing the presence and activities of arthropod consumers. The indirect regulation of elemental movement by arthropods is indicated by the hourglass-shaped valves on these flows.…

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from article Forest ecosystem

The southern pine beetle (Dendroctonus frontalis) is a destructive insect pest of coniferous forests in the southern United States. (Credit: U.S. Forest Service)

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from article Forest ecosystem

Belowground food web. (Credit: Elaine Ingham)

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from article Mycorrhizae

Example of a mycorrhizal association. The composite image shows the symbiotic relationship between a fly agaric mushroom (Amanita muscaria) and a birch tree (genus Betula). The mushroom receives sugar (C6H12O6) and oxygen (O2) from the tree and…

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from article Mycorrhizae

There are different types of symbiotic mycorrhizae. Ectomycorrhizae involve fungal hyphae that surround the cell walls of plant roots, but do not penetrate them. Endomycorrhizae involve fungal hyphae that penetrate the outer cells of plant roots.…

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from article Mycorrhizae

Cross section of several types of mycorrhizal fungi. (Credit: Modified from an original drawing by V. Furlan)

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from article Mycorrhizae

Ectomycorrhizae are characterized by a macroscopically visible fungal sheath that surrounds the plant root. (Credit: Robert L. Anderson/U.S. Department of Agriculture Forest Service)

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from article Fig

Panachée fig (Ficus carica). (Photo courtesy of David Karp, Agricultural Research Service, United States Department of Agriculture)

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from article Quinoa

Quinoa (Chenopodium quinoa). (Photo courtesy of Lisa Cyr)

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from article Quinoa

Structure of the major sapogenols of quinoa: oleanolic acid, hederagenin, and phytolaccagenic acid.

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from article Alder

Red alder (Alnus rubra), Mount Adams, Washington. (Photograph by Susan McDougall, USDA–NRCS PLANTS Database)

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from article Cubeb

Cubebs (Piper cubeba). (Photo courtesy of M. I. Ansari)

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from article Euthanasia

Euthanasia is an act by a person, typically a physician, actively and intentionally to end another person's life by some medical means at that person's explicit request. (Credit: Michael Jung/Shutterstock)

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from article Agricultural meteorology

A field of wheat. Like all crops, wheat requires a certain amount of water and a favorable temperate range in order to produce a good yield. (Credit: artush © 123RF.com)

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from article Mistletoe

European mistletoe (Viscum album). (Photo by Jan Samanek, State Phytosanitary Administration, Czech Republic)

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from article Oregano

European oregano (Origanum vulgare). (Photo courtesy of Leo Michels)

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from article Lawn and turf grasses

Tifway, which is a type of Bermuda grass, is a top-quality turf grass, often used on golf greens. (Photo by Jeff Vanuga, Natural Resources Conservation Service, U.S. Department of Agriculture)

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from article Lawn and turf grasses

Major lawn grass zones of the United States.

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from article Lawn and turf grasses

Dollar spot, which is caused by Sclerotinia homoeocarpa, often affects the appearance of various lawn and turf grasses, including creeping bentgrass. (Photo by Kevin Mathias, Agricultural Research Service, U.S. Department of Agriculture)

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from article Grape

Clusters of (left) common black grapes and (right) common red grapes (Vitis vinifera; subgenera Euvitis). (Photo by Patrick Tregenza, Agricultural Research Service, U.S. Department of Agriculture)

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from article Grape

Muscadine grapes (Vitis rotundifolia; subgenera Muscadinia). (Photo by David Nance, Agricultural Research Service, U.S. Department of Agriculture)

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from article Grape

The three main training–pruning systems used in California. (a) Head-trained–spur-pruned. (b) Cordon-trained–spur-pruned. (c) Head-trained–cane-pruned. (After R. J. Weaver, Grape Growing, John Wiley and Sons, New York, 1976)

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from article Grape

Slapper-type mechanical harvester. (After R. J. Weaver, Grape Growing, John Wiley and Sons, New York, 1976)

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from article Grape

Grape anthracnose (caused by Elsinoë ampelina), which is commonly called bird's-eye rot. (Photo courtesy of Clemson University, U.S. Department of Agriculture Cooperative Extension Slide Series; Bugwood.org)

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from article Grape

Downy mildew (caused by Plasmopara viticola) on a grape leaf. (Photo courtesy of the University of Georgia Plant Pathology Archive; Bugwood.org)

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from article Broccoli

Flower buds of broccoli (Brassica oleracea var. italica). (Photo courtesy of Forest and Kim Starr)

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from article Clove

Dried cloves, the unopened flower buds of Syzygium aromaticum. (Photo courtesy of Jorge Barrios)

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from article Beekeeping

A typical honeybee (Apis mellifera). (Credit: Stephen Ausmus/Agricultural Research Service, U.S. Department of Agriculture)

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from article Beekeeping

A pine tree cavity, which is a natural home for honeybees. (Credit: Georgia Forestry Commission, Dry Branch, Georgia)

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from article Beekeeping

Part of a colony of honeybees. Note the larger queen in the center of the photo. (Credit: Scott Bauer/U.S. Department of Agriculture Forest Service)

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from article Beekeeping

A typical wooden beehive. (Credit: Stephen Kirkpatrick/Natural Resources Conservation Service, U.S. Department of Agriculture)

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from article Beekeeping

A modern-day commercial apiary. Beekeepers often select apiary sites surrounded by woods so as to protect bees from damage by wind. In addition, secluded apiaries are less likely to be vandalized. (Credit: Carl Dennis/Auburn University, Alabama)

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from article Sphagnopsida