Allelopathic Chemicals:
Allelopathic chemicals are substances produced by one organism to protect against, or suppress, another organism.
(An alternative spelling is "alleopathy".)
Most allelopathic chemicals produced by trees are terpenes, phenolics, alkaloids or nitriles.
Kolines are chemicals made by one plant to suppress another plant’s growth.
(e.g. Walnuts produce juglone to suppress other plant species in their environs.)
Phytonicides are chemicals made by plants to suppress microorganisms.
Antibiotics are those chemicals used by one microorganism against another type of microrganism.
Angiosperm:
Members of the Kingdom Plantae with true flowers are the Angiospermae.
True flower have sepals, petals or other auxiliary structures surrounding the male (staminate) and female (pistillate) flower parts.
The ovule (ovum) is totally enclosed by tissues of the parent plant.
The sperm cell (in the pollen) must penetrate these cover tissues via a pollen tube to fertilise the ovule.
A seed is a fertilised ovule that has developed into an embryo, while still attached to the parent plant.
Primitively these plants are pollinated by insect vectors.
Wind pollinated angiosperms seem to have been derived from insect pollinated ancestors.
Likewise some angiosperms seem to have lost their sepals and petals.
Alga:
Algae are eukaryotic organisms which contain active chloroplasts.
Algae are basically the photosynthetic protoctists, and their macrophytic (seaweed) relatives.
(Cyanobacteria are no-longer considered an algal taxon.)
Algae belong to several taxonomic ranks, including: Chromista, Discicristata, Alveoles, Plantae and the Rhodophyta.
Some aglal species can grow in soils, or on plant tissues.
They are very seldom a direct problem in horticulture.
Bacterium:
Bacteria, Monera, or ‘bacters’, are single-celled organisms with a single cell-membrane.
Sometimes the cell is covered in a ‘cell-wall’ constructed of polysaccharides.
Bacteria lack a distinct nuclear membrane. (They are prokaryotes.)
The genetic material often consists of tiny DNA loops called ‘plastids’.
Bacteria are usually from 700 to 2000 nanometres in diameter.
(About one-tenth of a eukaryotic cell's diameter.)
They have wide variations in feeding behaviour, including photosynthetic autotrophs, and heterotrophs which feed-off other lifeforms.
Some live as single isolated cells, others cluster together, and still others form syncytial webs - almost like fungal hyphae.
The taxonomic disparity of the bacteria are extremely broad.
Parasitic forms of bacteria are significant causes of plant diseases.
But, other forms help to ‘fix’ nitrogen into a plant-useable form, and are thus of great benefit to plants.
Archaebacteria:
In the 1970s Carl Woese found that the ‘bacteria’ actually belong to two divergent taxonomic groups or ‘domains’.
These are the Archaea Domain and the Bacteria Domain.
The Archaea tend to live in anoxic water, hot-springs or other extreme conditions -
but they are not universally extremophiles.
Already it was noticed that the ‘archaes’ are more like eukaryotes in certain details.
In the early 2000s, T. Cavalier-Smith proposed that the Archaea and Eucaryota together form a clade, which he referred to as the Neomurans.
Despite their name, the Archaea are probably not really ‘older’ than other bacteria.
Cankers :
Cankers, in botanical parlance, are infected wounds in the cambium of plants.
A plant canker either does not heal over, or it heals over very slowly.
The wound may spread laterally, cutting off xylem and phloem sap flow, eventually killing the stem on which it occurs.
A wide range of organisms from bacteria, to oomycetes, to fungi can cause canker diseases.
Generally a canker infection starts at a small wound in the stem.
Some varieties within a species are more canker resistant than others.
Some of the most common canker fungi are ascomycetes in the Nectria genus.
Rose and pear cankers are usually caused by Nectria galligena.
Fusarium is a genus of basidiomycetes that can cause both wilts and cankers.
Chestnut blight and white pine blister rust are considered to be canker fungi.
Bacterial cankers are often caused by various species in the Pseudomonas genus.
Phytophthora fungoids can also cause serious cankers.
Canker Control:
Cankers should be controlled with treatments appropriate to the agent that causes them.
Use fungicides for fungal cankers, and bactericides for bacterial cankers.
Cankers, in some species, are not fatal.
Some trees totally recover.
Stems with cankers that are incapable of healing should be removed.
Pruning tools should be sterilised after working with cankers.
References:
Owen, D. and Adams, D. 2001. Impact of pitch canker on ornamental Monterey pines in Santa Cruz County, California, U.S., 1987-2000.
Journal of Arboriculture. 27(6): 298-305.
Holiday, Paul. 1989. A Dictionary of Plant Pathology. Cambridge University Press. New York.
Chytrid Moulds:
Chytridiomycota are a diverse group of fungi that are aquatic.
These moulds have apparently been around since the Cambrian Period.
They form both small fruiting bodies (thalli) and also mycelium.
These fungi often have gametes and asexual zoospores that are both flagellated.
Some chytrids are parasites, and others are saprobes.
Several are parasites on fungi, arthropods and even on animals.
The species in the order Blastocladiales are mostly saprobes.
Those in the order Chytridiales are more often parasites on terrestrial plants.
Some cause galls diseases on diverse species of plants.
One serious chytrid pest (Synchytridium endobioticum) causes the ‘black wart’ potato disease.
Conifers:
Conifers are the non-ginkgo and non-cycad gymnosperms.
They often have cone-like arrangements of seeds, and generally are monopodial with pointed crowns.
See also comments on urban conifers.
Cycads:
Cycads are Cycadophyta, they are gymnosperms.
Most have rosettes of frond-like leaves, with either male or female cones on the terminal ends of their stems.
Most living species are pollinated by beetle vectors.
They are all tropical, and were most diverse from the Carboniferous to Mesozoic.
Eelworms:
Nematodes are small vermiform animals in the Nematoda phylum.
Nematodes are also called ‘eelworms’ and ‘roundworms’.
They are anatomically simple protostomes with complete digestive tracts, no limbs and simple nervous systems.
Most are tiny to microscopic.
Many species can wait-out dry periods in cyst form.
Nematodes are a vast taxonomic group, with a huge range of niche specialisations.
Only a portion of the vast numbers of eelworm species are parasitic.
A few plant diseases are caused by nematodes, mostly these are the parasitic roundworms which afflict plant roots.
The worms are generally more of a problem for seedlings than for mature trees.
Eelworm Control :
In greenhouses, soil hygiene may be required to keep nematode infections at low levels.
Control measures may include soil fumigation.
Generally natural controls, including from other nematodes, keep the problem in check.
Eelworm Benefits :
Nematodes are, as often as not, beneficial to gardeners.
Many are carnivorous, and prey on garden pests.
Certain nematode species have even been pressed into service as biological control agents.
Eelworms are also the most fully studied of all animals, so far.
The soil eelworm Caenorhabditis elegans was the first animal to have its entire genome mapped by scientists.
Evergreens: Plants that retain live leaves through all seasons, including the winter. Evergreen is not synonymous with conifer, not all conifers are evergreen and vice versa. (Live oaks and hollies are evergreens.)
Ferns:
Ferns are a diverse group land plants in the Pteridophyta clade.
They are vascular plants which disperse by spores.
The spore upon contact with moist soil develops into a gametophyte.
The spermatozoa which arise from the gametophyte are flagellated, while the ovule remains enclosed in an archegonium - a case like structure on the gametophyte.
The diploid sporophyte stage, which grows from the fertilised ovule (zygote), is generally larger than the haploid gametophyte.
This larger sporophyte typically has long complex leaves (fronds) which bear many rows of spore-bearing bodies (sori).
Most ferns are small and herbaceous, but a few are tree-sized.
Fertiliser, NPK Formula:
Commercial fertilisers are usually labelled by their NPK percentages, i.e. the amount of the three major nutrients nitrogen (N), phosphorous (P) and potassium (K).
These elements are those most likely to be in short supply in soils.
The numbers in the NPK formula are the percentages by weight of each major nutrients in the mixture.
Nitrogen usually has the largest percentage in the mixture.
Nitrogen, in plant-useable form, is most often the element in low supply.
Some fertilisers have micronutrients added as well as N, P and K.
Fungi, Kingdom:
True Fungi are eucaryotes with chitin lined cell walls, that live by digesting food substances.
They are not directly photosynthetic*.
Cells tend to be syncytial, the cells run-together into long tube-like multi-nucleate 'hyphae'.
(Some Fungi are single celled, syncytial hyphae are not universal.)
Most fungi are isogametic, meaning that the 'male' and 'female' gametes are very similar in size and shape.
Fungi have many physiological and genetic similarities to animals.
The chytrid Fungi even have flagellated gametes, like animal spermatozoa.
Fungi often live in soil as saprobes, but some are parasites on other organisms, including plants.
Note: While not directly photosynthetic, many fungi live symbiotically with cyanobacteria, algae or plants.
Some glomeromycete moulds live in association with cyanobacteria.
Lichens and mycorrhizal fungi utilise plants' photosynthesis indirectly.
Of course, like animals even non-symbiotic fungi ultimately feed on plants, algae or cyanobacters.
Fungoids:
Fungoids are organisms which are like true Fungi in that they often have run-together (syncytial) cells, develop mycelium like strands, and are 'planted' in a substrate.
(Fungi were once considered plants because they are 'planted' in one place.)
They live by digesting food materials, and are not directly photosynthetic.
Unlike animals, they digest through their outer membranes.
Generally they grow like roots – growing in and penetrating their food source.
Some fungoids do not belong to the Fungi Kingdom.
Some, like the acrasiomycetes and labyrinthulids, seem more protozoan when examined in detail.
However, at the macro-level, they do seem to be very fungus-like in form and mode of growth.
The true Fungi, oomycetes, and the various slime moulds, could all be considered separate taxonomic clades.
Water moulds (Oomycota) include such fungoids as the Phytophthora blights and the damping-off Pythium.
Galls: Galls are localised abnormal growths on plants, the development of which is stimulated by a parasitic organism.
Some insects and mites stimulate the formation of galls when they lay their eggs.
The tissues of the gall are used to feed the larvae.
(Some fungi can also cause gall formation.)
Galls are caused by a re-routing of normal developmental processes.
This is why gall tissues are homologous with the tissues in normal plant organs.
The fibrous-masses of bedegaur galls on rose stems are caused by the Diplolepis rosae wasp.
Woody balls, or swollen stem galls, on roses can be the larval chambers of Diplolepis spp. wasps.
Black currents’ big bud galls are instigated by Cecidophyopsis ribis mites.
The hallow apple galls on oak leaves are instigated by cynipid wasps in the Andricus, Biorhiza and Neuroterus genera.
Small papillae, pouch or bead galls on leaves are often caused by mites in the Aculops, Aculus and Eriophyes genera.
The pine-apple galls on spruce and fir house the larvae of Adelges abietis, an adelgid insect.
The cone-like strobilary galls on willows support Rhabdophaga strobiloides fly larvae.
Graft-Transmissible Agents:
The term 'graft-transmissible agent' refers to plant diseases that can be transmitted by grafting, or contact between plants, just like a virus.
Specifically, the term is restricted to those disease agents that have not been positively identified as either viral or bacterial.
Read about graft-transmissible agents.
Growth Regulators:
Phytohormones are now generally called ‘growth regulators’.
Growth regulators are chemical signals used to communicate from one tissue type to another.
Like true hormones they are signals, and do not directly cause the responses they stimulate.
Also like hormones they tend to counteract one-another.
The balance of these counteractions keeps the growth of tissues co-ordinated.
Gymnosperm:
Vascular Plantae, which bear true seeds, and have exposed ovules, are considered Gymnospermae.
The ovule (ovum) is exposed and is directly contacted by the pollen during fertilisation.
A seed is a fertilised ovule that has developed into an embryo, while still attached to the parent plant.
Gymnosperm is an informal group, which includes ginkgos, cycads and conifers.
Horsetails:
Horsetails, also called ‘scouring-rushes’, or the Sphenophyta, are true vascular plants.
All sphenophytes, nowadays, belong to the genus Equisetum.
They all have segmented shoots, with whorls of segmented side ‘branches’.
They have silica nodules in their stems.
Horsetails are spore-bearing plants with both sporophyte (diploid) and gametophyte (haploid) generations.
Gametophytes are very tiny, and tend to be either male or female.
The male gamete (antherozoid) is a ciliated ‘sperm cell’.
The sporophyte is the larger generation.
Strangely, there are usually two different sporophyte forms.
‘Sterile’ stems have a purely photosynthetic role.
These sterile forms store carbohydrates in rhizomes for the ‘fertile’ forms, which may appear later in the season.
The cone-like strobilus (sporocarp) is at the apex of the fertile stem.
Most horsetails are temperate plants of moist bottomlands.
In the Paleozoic certain species of horsetails, and clubmosses also, attained full tree size.
Horsetail weeds :
Horsetails are considered by farmers to be weeds.
On the other hand, they may also be planted on purpose as ornamentals!
They can compete with crop plants, but are usually not a severe problem for trees.
Horsetails are somewhat poisonous to livestock.
Lichen:
Lichens are a classic example of symbiosis.
They are fungi which encase algae. The algae are photosynthetic and produce carbohydrates.
The fungi utilise the carbohydrates for energy, and play host to the algae.
Lichen fungi feed the algae, and protect them from desiccation.
The algae can be either eukaryotic or cyanobacterial. The combination is wonderfully effective.
Lichens can grow near glacier edges, on mountains, on rock faces, on dead trees, and other locations that are normally hostile to plants, fungi or algae.
'False' pixie-cup, on forest floor & Physciella lichens on tree bark.
One might suppose that such a perfect form of symbiosis, as lichens exhibit, could only have but one origin.
In the early 1990s A. Gargas et al subjected lichen fungi to DNA analysis.
The results were surprising. The ‘true’ lichen fungi fell into at least five separate lineages.
Each lichen lineage had close relatives that were not lichens.
For example, the Lichenomphalia were found to be more closely related to the Pleurotus mushrooms than to the Multiclavula lichens.
That is, the lichen lifeform was invented by nature several times. The fruiting bodies of these lichens hint of their disparate origins.
Most ascomycete lichens have apothecia, whereas the basidiomycete lichens sprout little gilled toadstools.
Lichens have existed since the Devonian, and probably even earlier.
The fossils suggest that many of these early lichens were ascomycetes.
A significant portion of these asco-lichens appear to have had a common ancestor - that was also a lichen fungus.
There is evidence that many kinds of mould-fungi were derived from lichen ancestors!
That is, lichens may have evolved into non-symbiotic moulds through a loss of their photobionts.
Many of these moulds probably began to feed on external algae, or to feed on the exudes of plant roots.
Some seem to have become 'endolichenic' fungi. They parasitise the algae inside lichens.
Some pin-moulds form lichen-like associations.
The Glomeromycota are a clade of pin-moulds best known for their role as endomycorrhiza.
A few of the glomeromycetes also have symbiotic relationships with algae.
In particular, the Geosiphon pyriformis is a small pin-mould.
Its hyphae can contain Nostoc cyanobacteria.
These bacteria are enclosed inside its cells in a manner most unlike ‘normal’ lichens.
These moulds are usually not considered to be ‘true’ lichens.
References:
Baringa, Marcia. 1995. Origins of lichen fungi explored. Nature. Vol. 268 (9): 1437.
Gargas, Andreas, DePriest, Paula T., Grube, Martin & Tehler, Anders. 1995. Multiple origins of lichen symbioses in fungi suggested by SSU rDNA phylogeny. Nature. 268 (9): 1492-1495.
Kluge, M. 2002. A fungus eats a cyanobacterium: the story of the Geosiphon pyriformis endocyanosis. Biology and Environment: Proceedings of the Royal Irish Academy. 102 (1): 11-14.
Lutzoni, F. and Miadlikowska, J. 2009. Lichens. Current Biology. 19 (13): 502-503.
Schüßler A, Schwarzott D, and Walker C. 2001. A new fungal phylum, the Glomeromycota: phylogeny and evolution. Mycological Research. 105 (12): 1413-1421.
Taylor, T.N. Hass, H., Remy, W. and Kerp, H. 1995. The oldest fossil lichen.
Nature, 378: 244.
Taylor, T.N., Hass, H. and Kerp, H. 1997. A cyanolichen from the Lower Devonian Rhynie chert. American Journal of Botany. 84(8): 992-1004.
Micronutrients:
Some elements are required by plants in relatively small amounts.
Usually, these trace elements are essential to plant survival.
However, even very poor soils often have enough of these elements for plant survival.
Micronutrients include: iron (Fe), manganese (Mn), boron (B), copper (Cu), molybdenum (Mo), and for some plants even aluminium (Al) and selenium (Se).
Mosses:
‘Moss’ is a rather vague term for small cushiony plants.
Gardeners use the word ‘moss’ to mean: liverworts, bryophytes or clubmosses.
These plants are all members of the Kingdom Plantae which disperse via spores.
They have alternate gametophyte (haploid) and sporophyte (diploid) generations.
The male gamete is flagellated and the female gamete is egg-like (ovule).
Liverworts and bryophytes are said to be ‘non-vascular’.
Clubmosses are true vascular plants.
True mosses have dominant gametophyte generations, and the clubmosses have dominant sporophytes.
Most types of moss grow best in moist shady areas.
Consequently, growth of moss in gardens is often associated with deeply shaped damp areas.
Moss may be a symptom of excess moisture.
Excessive moisture can instigate mildews, moulds and cankers.
Moss usually causes no harm in itself.
Moss Control :
One should not bother controlling moss by adding lime, et cetera, to increase soil pH.
It is mostly the excess shade, not the pH, which causes moss to dominate a lawn.
Mycorrhizae:
The symbiotic combination between soil fungi and plant roots is known as mycorrhizae.
Vascular plants commonly have a symbiotic relationship with fungi.
In this relationship the fungal mycelia intertwine with the rootlets of plants.
Roots can absorb water and highly soluble minerals.
Fungi are generally better at absorbing low mobility ions, such as phosphorous, than are plants.
Mycorrhizal fungi gain sugar from the roots of plants and, as if by way of trade, pass disolved minerals to the plants' rootlets.
Read about mycorrhizae & symbiosis.
Mycosomes :
Mycosomes are small spore-like fungal propagules found in many plant cells.
For the most part they are opportunistic saprobes that ‘awake’ when a host cell starts to die. Mycosomes can transform into yeast-like cells given the right stimuli.
Several known kinds of fungi have been found to have a hitherto unrecognised mycosome phase.
Like nanobacteria, a degree of scepticism is called for.
Some reports of mycosomes have been mistaken.
Atsatt, Peter R. 2003. fungus propagules in plastids: the mycosome hypothesis. Int. Microbiol. 6: 17-26.
Nanobacteria:
Nanobes, nannobacteria or nanobacteria are terms originally applied to very small bacteria less than 0.1 micrometres (100 nanometres) wide.
In the 1990s a number of scientist claimed to have found tiny bacters in the virus size range.
Some early 'sightings' of nanobes were based on mistaken idenification.
Even bacteriology has its Loch Ness monsters.
Most of the early alleged examples of nanobes were clearly too small to contain even a few ribosomes, let alone the other machinery of life.
In the late 1990s some examples of very small bacters (0.1 to 0.3 microns) were confirmed.
These were basically small versions of mycoplasma and phytoplasma.
Some thermoplasmas, found in hotsprings, can be as small as 0.3 microns wide.
Functional genomes and ribesomes exist inside these tiny bacters.
Recent research suggests that nanobacteria are often in fact not living things.
In particular the nanobes that ‘cause’ kidney stones are probably not really ‘alive’ per se.
Rather, they often seem to mineral-fetuin complexes.
Fetuin proteins normally function in animals to stop crystallisation.
Under certain conditions the proteins form complexes with minerals - instead of stopping crystals from forming.
They are self-replicating, so they have some semblance to living-things.
References: Taylor, Michael Ray. 1999. Dark Life. Scribner. New York.
Raoult D, Drancourt M, Azza S, Nappez C, Guieu R, et al. (2008) Nanobacteria Are Mineralo Fetuin Complexes. PLoS Pathog 4(2): e41
Nematode: For information on nematodes, see
eelworms.
Nitrogen fixation:
Many free-living bacteria have the ability to ‘fix’ nitrogen from the air.
They can transform di-nitrogen gas from the air into soluble and useable nitrogen-compounds.
Many plants utilise these bacteria symbiotically – they use the bacteria to obtain extra nitrogen for themselves.
Some grasses use nitrogen fixing Azotobacter bacteria.
Many plants, like the legumes, host Rhizobium bacters in specialised root nodules.
Alders, casuarinas, and some other plants, host nitrogen-fixing Frankia bacteria.
Oömycota:
Oömycetes, ‘egg fungi’, or ‘water moulds’, are organisms which are superficially like fungi in having syncytial hyphae.
Unlike fungi, their cell walls are composed of cellulose.
They are clearly different from fungi at a taxonomic level above Phylum.
They are now classified as being in the Division Oömycota within the Chromista Kingdom.
Sometimes this Kingdom is referred to as the Stramenophila.
Oomycetes are genetically closer to seaweeds than to the true Fungi.
Like these algae, oomycete zoospores often have two flagella.
Asexual diploid zoospores are utilised for dispersal.
(The opposite of the chytrid fungi.)
Many species are fully aquatic, others can live in soil.
Sexual fusion, of haploid gametes, takes place at the meeting of sexual hyphae.
These fused hyphae produce a distinctive ball-like ‘oospore’.
There are both saprobic and parasitic species.
Some damping-off moulds, downy mildews, and the various phytophthora blights, are caused by oomycetes.
One strain of phytophthora causes sudden oak death.
The common Saprolegnia are soil and water fungoids, a few of which are parasites.
Organic Chemistry:
‘Organic chemistry’ is the branch of chemistry science dealing with compounds that contain carbon, nitrogen and oxygen.
It retains the name ‘organic’ because before the nineteenth century it was thought that only biota could create the complex compounds associated with living things.
Nowadays it is accepted that simple organic compounds can be formed by abiotic means.
For example, carbonaceous chrondrite meteorites contain simple ‘organic’ compounds.
Organic Farming & Gardening:
Organic farming and gardening practices attempt to mimic ‘natural’ eco-dynamics in the context of horticulture and animal husbandry.
That is, an attempt is made to recycle nutrients within a farm or garden.
Organic farmers/gardeners try to minimise the use of fertilisers of external origin.
Sometimes ‘organic’ farmers endeavour to avoid all fertilisers or pest controls that are factory made or ‘synthetic’.
(In practice, some factory fixed nitrogen is necessary.)
Organic Pest Management:
Organic farmers and gardeners attempt to avoid the use of ‘artificial’ methods of pest control.
Pesticides that are biotic in origin are preferred over those made in a factory.
Likewise there is an emphasis on organic pest management (OPM).
This mode of pest control strives to utilise indigenous biotic pest control agents.
That is, conditions for native predatory organisms are enhanced so as to keep the pest organisms in check.
Organic farming/gardening is not without its critics.
For starters, the cliché equation of ‘natural’ with ‘good’ is too overblown.
The more scientific approach to organic farming/gardening is to attempt to minimise deleterious impacts of the farming/gardening on the surrounding ecosystems.
Sometimes specific synthetic fertilisers/pesticides are the more eco-friendly option.
References:
Harris, Marjorie. 1996. Ecological Gardening. - your path to a healthy garden. Random House Canada. Toronto.
Bradley, F.M. and Ellis, B.W. 1992. Rodale's All-New Encyclopedia of Organic Gardening. Rodale Press. Emmaus PA.
Silver, Lee M. 2007. The Clash of Biotechnology and Post-Christian Spirituality. Skeptical Inquirer. 31 (2): 32-37.
Organic material:
Organic matter in soil is the non-decomposed material of biotic origin.
It is sometimes called ‘humus’.
Paradoxically in robust ecosystems, such as rainforests, organic matter has a brief sojourn in the soil before it is recycled.
In sluggish ecosystems, such as tundra, deep layers of humus can accumulate.
Soils types vary greatly in the amount of humus that they contain.
Generally the more organic matter in the soil the easier it is for plants to grow.
If the organic layer is too thick, some of the nutrients can become too diluted or washed-out.
Phosphorus is often lacking in the extreme histosolic humus of peat bogs.
Palms - Palmae:
Palms are members of the Arecaceae family.
(Formerly called Palmae.)
These monocots vary from vines, to small shrubs, to trees.
They do not have annual rings, the mixed phloem and xylem bundles expand as they grow to full girth.
They are usually monopodial with frond-like leaves, and flowers, on the terminal end.
Living examples are warm temperate to tropical.
Phytohormones:
Growth regulators are chemical signals used in plants to co-ordinate growth and development.
Growth regulators were once called 'phytohormones'.
They are much like hormones in that they function as signals between tissues.
Auxins are growth regulators which are produced in apical meristems and leaves, they stimulate root growth.
Gibberelins are produced primarily in roots, they stimulate leaf growth.
Cytokinins are made largely in root apices, and they signal meristem growth.
Abscisic acid is produced primarily in old leaves, and fruit, it promotes dormancy in other tissues.
Ethylene is produced in wounded tissue, it stimulates tissues outside the wound to aid in healing.
These phytohormones usually stimulate, or inhibit, growth in tissues other than those in which they are made.
These interactions ensure that different tissues do not grow out of balance with each other.
Plant:
'Plant' is a colloquial term for those organisms which lack independent locomotion, and have a nutritive system based on photosynthesis.
This group includes both land plants and seaweeds.
Other 'planted' organisms like the Fungi and fungoids are sometimes called 'plants' because they are immobile.
Plantae, Kingdom:
The Kingdom Plantae consists of those eucaryotes with cellulose cell walls,
which have intracellular chloroplast organelles that photosynthesise via chlorophyll and liberate dioxygen (O2) in the process.
They also store the starch made by photosynthesis inside the chloroplasts*.
Multicellular Plantae are very similar, at a cellular level, to green algae (Chlorophyta).
Some green algae are single celled and mobile.
(These green algae are genetically much closer to 'higher plants' than to the other clades of protozoa.)
The Chromista algae are photosynthetic also, but they differ from Plantae in the details of their starch storage and photosynthesis.
These chromist algae are nowadays often classed as separate taxa.
Since the red algae (Rhodophyta) are genetically somewhat close to green plants, they are sometimes included in the Plantae Kingdom.
In the latest taxonomic system, the rhodophytes, glaucophytes, green algae and plants are included in the Super-Group Archaeplastida.
* Note: There are non-photosynthetic Plantae that live as parasites, and also there are plants which exploit mycorrhizal fungi without benefit to the fungi (e.g. some orchids).
These plants probably were derived from photosynthetic ancestors.
Protozoon:
A protozoon is a ‘primative’ (proto) animal (zoon) like creature.
Protozoa are usually either unicellular, or simple colonies of cells.
Roughly speaking, if the creature is photosynthetic it is an alga, if it is heterotrophic it is a protozoon.
Many protozoa have one or more undulipodia (flagella), others are amoeboid, still others have both traits!
There are protozoan members in every taxonomic ‘Kingdom’ of eukaryote.
Some of the fungoid protozoa are parasites in plant tissues.
Kingdom Protozoa:
In past decades taxonomists had defined the Protozoa as a taxonomic ‘kingdom’ or ‘regnum’.
Under such nomenclature the Kingdom Protozoa does not usually include those algae and seaweeds that are in the Kingdom Chromista.
Some older taxonomic schemes lumped the protozoa, algae and seaweeds into the Kingdom Protoctista.
Either way, the word ‘protozoa’ can be used in its colloquial sense - such as to include algae.
Rust Fungi:
‘Rusts’ are fungi in the Uredinales order.
Usually they are microfungi, on the edge of being visible to the human eye.
Commonly they have rusty-reddish spore-bodies.
A patch of these reddish spore-bodies may look like ‘rust’.
These fungi are unusual in tending to have alternate host plants.
The hosts can be in widely different plant families.
Rust fungi also may have more than two distinct types of spores.
(Fungi typically have two kinds of spores.)
Asexual spores may come in two types.
The aeciospores and the urediniospores may be quite different in structure, and different in the shape of their fruiting bodies.
They may even occur on different host species!
The sexual (haploid) teliospores germinate into spermatial hyphae.
These hyphae may yet produce a round of sexual pycnidiospores, before the actual fusion of the gametes occurs.
Common rust genera include the Puccinia, Uromyces, Melampsora, Cronartium and Gymnosporangium.
Rust Control: Rust fungi are best controlled by distancing the alternate host plants, as far as this is a practical option.
Fungicides have limited efficacy against rust diseases.
Slime Mould:
Several different types of organism can produce visible blobs on the ground, or on surfaces.
These are the 'slime moulds' (slime molds).
Bacterial, plasmodial, and cellular slime moulds can all produce distinct gelatinous blobs on grass, leaf duff or organic soil.
Slime moulds are peculiar in that separate cells migrate together to form a plasmodium,
this jelly-like mass transforms into a spore bearing body, or sometimes into a troop of fruiting bodies.
Some slime moulds have cells which swarm together, but do not fuse (Dictyostelida).
Others have cells which fuse into a single multi-nucleate plasmoidium (Myxogastria).
Slime moulds are classified into five, or six, mutually distant taxonomic groups.
'Slime mould' is a life form (ecological strategy) not a taxonomic category.
However, most slime moulds are in the Myxogastria group, i.e. they are Amoebozoa.
Fruiting bodies of a slime mould.
Swarm cells, plasmodial phase, aethalium, and sporocarp.
Except for the myxobacteria, all of the slime moulds were once considered to be in the Fungi Kingdom.
Nowadays it is recognised these moulds are not all even in the same taxonomic kingdom as one another!
The plasmodiophoromycetes are closer to foraminferans than to the fungi.
The acrasiomycetes are closer to the euglenoid flagellates than to the fungi.
This is similar to the status of the ‘slime-nets’ (labyrinthulomycetes), and ‘water moulds’ (oomycetes), which were also once mistaken for types of fungi.
Slime moulds are mostly saprobic or bacterivorous.
The endoparasitic slime moulds are mostly a problem for herbaceous plants.
Aside from nutrient competition and accelerating mulch decay, most slime moulds do not directly harm trees.
Reference:
Stephenson, Steven L. and Stempen, Henry. 1994. Myxomycetes – a handbook of slime molds. Timber Press Inc. Portland, Oregon.
Stress:
‘Stress’ is a somewhat overly anthropomorphic word.
Nevertheless, the idea of plant weakening due to ‘stressful’ conditions has some meaning.
A plant must allocate its resources to a limited number of tasks.
Consider the example of water stress in relation to disease resistance.
If too many of its resources are being used to remedy one disorder, it may not be able to allocate resources to fight a disease agent.
Thus, if a plant is subject to drought, more of its stored carbohydrates are used to grow feeder roots.
Thus it may be able to afford less energy in the synthesis of defensive compounds.
Thus it is said that a plant ‘stressed’ by lack of water becomes ‘weaker’ in its self-defence against insects.
Smut Fungi:
Smut moulds are fungi in the Order Ustilaginales.
Often they form spot-like fruiting bodies on leaves or stems.
A few instigate deformities in the host’s tissues.
These fungi are mostly a problem for non-woody plants.
Copper based fungicides are some what effective against them.
Choosing smut-resistant cultivars is a more efficacious method of control.
Soft Rot:
Soft Rot is a generalised name for rots that destroy plant tissues.
Most are moulds (eg Choaenephora), though some are bacterial (eg Erwinia).
Usually they are opportunistic infections that are exacerbated by overly moist conditions.
Stressed plants also are more prone to the problem.
Symbiosis:
Symbiosis is the co-existence of two different species, each of which mutually benefits the other.
Read about symbiosis.
Wilt Diseases:
‘Wilt’ is a catch-all term for a set of fungal diseases which can cause vascular blockage, and consequently result in leaf wilting.
Wilt fungi may be Fungi Imperfecti, ascomycetes or basidiomycetes.
Ophiostoma novo-ulmi or ‘Dutch elm disease’ is a wilt.
The genus Verticillium is another common source of wilt fungi.
Wilt Control :
Wilts are generally difficult to control.
Organisms inside the xylem of plants are not easily accessed by fungicides, without also injuring the plant.
Planting wilt resistant varieties is one option for reducing wilt incidence.
Xylella:
Xylella are a genus of bacteria that can cause leaf scalds and leaf scorches.
Mostly the Gram negative bacteria infect xylem.
Elms, mulberries, oaks, plane-trees, and the prunus species, are prone to xylella scalds.
Xylella scalds can be reduced with bactericide application - but not easily cured.
Yeast:
Yeast is a single celled fungus.
Unicellular fungi occur in diverse taxonomic groups.
Though not usually disease agents, some of the soft rots of corms and bulbs (eg. Kluyveromyces) are yeast fungi.
Otherwise yeasts are mostly just agents of decay, and not usually pathogens.
