Lichens Sentence Examples
Still, the reindeer frequents it for its lichens, and on the drier slopes of the moraine deposits there occur four species of lemming, hunted by the Arctic fox (Vulpes lagopus).
Lichens for the herbarium should, whenever possible, be sought for on a slaty or laminated rock, so as to procure them on flat thin pieces of the same, suitable for mounting.
The majority of the lichens, however, possess a stratified thallus in which the gonidia are found as a definite layer or layers embedded in a pseudoparenchymatous mass of fungal hyphae, i.e.
The cortical layer is usually more developed on the side towards the light, while in many lichens this is the only side provided with a cortical layer.
Funf stuck gives ten free living algae which have been identified as the gonidia of lichens.Advertisement
We find two chief types of fruit bodies in the lichens, the perithecium and apothecium; the first when the fungal element is a member of the Pyrenomycetes division of the Ascomycetes, the second when the fungus belongs to the Discomycetes division.
Cytological details of nuclear behaviour among the lichens are, however, difficult to obtain owing 'to the slow growth of these forms and the often refractory t' nature of the material in the matter of preparation for microscopical ex amination.
As is clear from the above, nearly all the lichens are produced by the association of an ascomycetous fungus with algae.
For some obscure reason the Basidiomycetes do not readily form lichens, so that only a few forms are known in which the fungal element is a member of this family.
Lichens are found growing in various situations such as bare earth, the bark of trees, dead wood, the surface of stones and rocks, where they have little competition to fear from ordinary plants.Advertisement
As is well known, the lichens are often found in the most exposed and arid situations; in the extreme polar regions these plants are practically the only vegetable forms of life.
The life of many lichens thus consists of alternating periods of activity when moisture is plentiful, and completely suspended animation under conditions of dryness.
Though so little sensitive to drought and extremes of temperature lichens appear to be very easily affected by the presence in the air of noxious substances such as are found in large cities or manufacturing towns.
The growth of lichens is extremely slow and many of them take years before they arrive at a spore-bearing stage.
The chemistry of lichens is very complex, not yet fully investigated and can only be very briefly dealt with here.Advertisement
Calcium oxalate is a very common substance, especially in crustaceous lichens; fatty oil in the form of drops or as an infiltration in the membrane is also common; it sometimes occurs in special cells and in extreme cases may represent 90% of the dry substance as in Verrucaria calciseda, Biatora immersa.
The classification of lichens is unique in the fact that chemical colour reactions are used by many lichenologists in the discrimination of species, and these reactions are included in the specific diagnoses.
A similar relation between oil formation and the nature of the substratum has been observed in many lichens.
In the arts, as food and as medicine, many lichens have been highly esteemed, though others are not now employed for the same purposes as formerly.
Lichens Used in the Arts.Advertisement
Amongst other lichens affording red, purple or brown dyes may be mentioned Ramalina scopulorum, Parmelia, saxatilis and P. omphalodes, Umbilicaria pustulate and several species of Gyrophora, Urceolaria scruposa, all of which are more or less employed as domestic dyes.
These pigments primarily depend upon special acids contained in the thalli of lichens, and their presence may readily be detected by means of the reagents already noticed.
During the middle ages, and even in some quarters to a much later period, lichens were extensively used in medicine in various European countries.
Zukal has considered that the lichen acids protect the lichen from the attacks of animals; the experiments of Zopf, however, have cast doubt on this; certainly lichens containing very bitter acids are eaten by mites though some of the acids appear to be poisonous to frogs.
Theoretically the lichens may be classified on the basis of their algal constituent, on the basis of their fungal constituent, or they may be classified as if they were homogeneous organisms. The first of these systems is impracticable owing to the absence of algal reproductive organs and the similarity of the algal cells (gonidia) in a large number of different forms. The second system is the most obvious one, since the fungus is the dominant partner and produces reproductive organs.Advertisement
There are two main divisions of lichens, Ascolichenes and Basidiolichenes, according to the nature of the fungal element, whether an ascomycete or basidiomycete.
Sometimes various lichens occur abnormally in such unexpected habitats as dried dung of sheep, bleached bones of reindeer and whales, old leather, iron and glass, in districts where the species are abundant.
It is apparent that in many cases lichens are quite indifferent to the substrata on which they occur, whence we infer that the preference of several for certain substrata depends upon the temperature of the locality or that of the special habitat.
Thus in the case of saxicolous lichens the mineralogical character of the rock has of itself little or no influence upon lichen growth, which is influenced more especially and directly by their physical properties, such as their capacity for retaining heat and moisture.
As a rule lichens grow commonly in open exposed habitats, though some are found only or chiefly in shady situations; while, as already observed, scarcely any occur where the atmosphere is impregnated with smoke.
It is to the different characters of the stations they occupy with respect to exposure, moisture, &c., that the variability observed in many types of lichens is to be attributed.
In arctic regions lichens form by far the largest portion of the vegetation, occurring everywhere on the ground and on rocks, and fruiting freely; while terrestrial species of Cladonia and Stereocaulon are seen in the greatest luxuriance and abundance spreading over extensive tracts almost to the entire exclusion of other vegetation.
In intertropical regions lichens attain their maximum development (and beauty) in the foliaceous Stictei and Parmeliei, while they are especially characterized by epiphyllous species, as Strigula, and by many peculiar corticole Thelotremei, Graphidei and Pyrenocarpei.
To give any detailed account, however, of the distribution of the different genera (not to speak of that of individual species) of lichens would necessarily far exceed available limits.
Some of the species look more like lichens than flowering plants.
On the other hand, lichens, previously regarded as autonomous plants, are now known to be dual organisms - fungi symbiotic with algae.
The excluded genera are distributed among the liverworts, lichens and fungi; but notwithstanding the great advance in knowledge since the time of Linnaeus, the difficulty of deciding what limits to assign to the group to be designated Algae still remains.
Peysonellia squamaria, Melobesia lichenoides, Leathesia difformis are forms which are not attached throughout but grow in plates like the foliaceous lichens.
The play of colour is exquisite, the basalt combining every tint of warm red, brown and rich maroon; sea-weeds and lichens paint the cave green and gold; while the lime that has filtered through has crusted the pillars here and there a pure snow-white.
Elsewhere even the leaved lichens are precarious, though the leather lichens flourish.
Lichens and mosses clothe many of the boulders that are scattered over the upper slopes.
There are innumerable kinds of moss and lichens and ferns with leaves 12 ft.
The birch and larch woods of this zone give way to pine forests as the altitude increases; and the pines to mosses, lichens and alpine plants, just below the jagged iron-grey peaks, many of which attain altitudes of 6000 to 8000 ft.
Covered with snow for the greater part of the year, and growing nothing but lichens, mosses and some scanty grass, the South Shetlands are of interest almost solely as a haunt of seals, albatrosses, penguins and other sea-fowl.
About one tenth of the land is covered by forests, which give place, at an altitude of 5000 ft., to lichens and mosses.
The writer is not aware of any evidence for the occurrence of Palaeozoic Lichens.
Concentrations of lead, zinc, cadmium and other heavy metals in lichens and marine bivalves are measured.
Forms of scree dominated by bryophytes and lichens have also been taken into account in site selection.
The wood contains a rich variety of plants and includes a number of notable bryophytes and lichens.
Look for plants such as sea pink, moss campion, scurvy grass, sea mayweed and lichens on the rocky foreshore.
In high summer, the dried lichens and mosses give the dunes a very crunchy texture, which is almost like walking on crisps.
Lichens, especially species of the diverse genus Cladonia, are a very important group on heathland.
Most lichens that contain green algae can recover from drought by absorbing water from humid air and then begin to photosynthesise.
The heathland is rich in lichens, including the rare golden hair lichen.
Humans have a long history of using lichens for different purposes.
In East Devon, we have some very rare lichens dependent on trees, particularly on ash.
The woods have an exceptional diversity of rare epiphytic lichens.
These are not the only tar lichens present on the shore and they are difficult to distinguish from each other.
Limpets (Patella vulgata) and rough periwinkles are snails that graze on the algae and lichens.
Repair or build a drystane dike to provide shelter for animals and plants such as wall rue, lichens or mosses.
The southern part is dry, with poor bog moss cover, short common heather, deer sedge, cross-leaved heath and Cladonia lichens.
Plants include wood sorrel, wood anemone and a wide variety of mosses, lichens and fungi.
Estuarine Lichens (Link) 2 February 2005 On the Adur at mid-tide, two Little Grebes were diving underwater near Cuckoo's Corner.
Long lichens hung off spring leaves, the temperature rose and we entered a wonderland of greenery.
The group has until recent years been regarded as comprising three classes distinguished by well-marked physiological featuresthe Algae (including the Seaweeds) which contain chlorophyll, the Fungi which have no chlorophyll and therefore lead a saprophytic or parasitic mode of life, and the Lichens which are composite organisms consisting of an alga and a fungus living together in a mutual parasitism (symbiosis); Bacteria were regarded as a section of Fungi.
It has however been deemed advisable to retain the older groups for purpose of treatment in this work, and articles will be found under the headings ALGAE, FUNGI, BACTERIA, and LIcHENs.
Owing to the similarity of structure and mode of life it is convenient to treat the Lichens (q.v.) as a distinct class, while recognizing that the component fungus and alga are representatives of their own classes.
This form of relationship is now known in other groups of plants (see Bacteriology and Fungi), but it was first discovered in the lichens.
Such are sugars (glucose, mannite, &c.), acids (acetic, citric and a whole series of lichen-acids), ethereal oils and resinous bodies, often combined with the intense colours of fungi and lichens, and a number of powerful alkaloid poisons, such as muscarin (Amanita), ergotin (Claviceps), &c.
The remarkable case of life in common first observed in lichens, where a fungus and an alga unite to form a compound organism - the lichen - totally different from either, has now been proved to be universal in these plants, and lichens are in all cases merely algae enmeshed in the interwoven hyphae of fungi (see Lichens).
As it flows it takes the forms of sappy leaves or vines, making heaps of pulpy sprays a foot or more in depth, and resembling, as you look down on them, the laciniated, lobed, and imbricated thalluses of some lichens; or you are reminded of coral, of leopard's paws or birds' feet, of brains or lungs or bowels, and excrements of all kinds.
A set of 5 identification leaflets to the common saxicolous lichens in lowland England is available from Ivan Pedley (cost £ 3.00).
Estuarine Lichens (Link) 2 February 2005 On the Adur at mid-tide, two Little Grebes were diving underwater near Cuckoo 's Corner.
The bark of tupelos is roughly furrowed, so that it is often the host for mosses and lichens.
Traditionally, the cloth was colored with dyes made from local plants and lichens, which gave it its distinctive outdoors look.
This is especially the case in the lichens (symbiotic organisms composed of a fungal mycelium in association with algal cells), which are usually exposed to very severe fluctuations in external conditions.
This is particularly marked in certain lichens of shrubby habit.
Since about 1880 our knowledge of the species which can enter into such relationships has been materially extended, and the fungal constituents of the Lichens are known to include Basidiomycetes as well as Ascomycetes.
In the Florideae, Lichens and Laboulbenjaceae the, male cell is a non-motile spermatium, which is carried to the female organ.
They feed chiefly on grass, but also on moss, lichens and tender shoots of the willow and pine.
Lichens are generally mounted on sheets of paper of the ordinary size, several specimens from different localities being laid upon one sheet, each specimen having been first placed on a small square of paper which is gummed on the sheet, and which has the locality, date, name of collector, &c., written upon it.
Many lichens, such as the Verrucariae and Collemaceae, are found in the best condition during the winter months.
Those fungi which are of a dusty nature, and the Myxomycetes or Mycetozoa may, like the lichens, be preserved in small boxes and arranged in drawers.
Below the mountain crests, where only the hardiest lichens and mosses can survive, comes a belt of large timber, including many giant trees, 200 ft.
The rocks of which these various monuments are composed is the ordinary granite of the district, and most of them present a strange appearance from their coating of white lichens.
The last trees which struggle for existence on the verge of the tundras are crippled dwarfs and almost without branches, and trees a hundred years old are only a few feet high and a few inches through and thickly encrusted with lichens.'
In the alpine tracts of the north the narrowness of the valleys and the steep stony slopes strewn with debris, on which only lichens and mosses are able to grow, make every plot of green grass (even if it be only of Carex) valuable.
The flora consists of 129 species of angiosperms, i Cycas, 22 ferns, and a few mosses, lichens and fungi, 17 of which are endemic, while a considerable number - not specifically distinct - form local varieties nearly all presenting Indo-Malayan affinities, as do the single Cycas, the ferns and the cryptogams. As to its fauna, the island contains 319 species of animals-54 only being vertebrates-145 of which are endemic. A very remarkable distributional fact in regard to them, and one not yet fully explained, is that a large number show affinity with species in the Austro-Malayan rather than in the Indo-Malayan, their nearer, region.
Impure inactive forms result on the polymerization of glycollic aldehyde and also on the oxidation of erythrite, a tetrahydric alcohol found in some lichens.
It is found in the form of its acid potassium salt in many plants, especially in wood-sorrel (Oxalis acetosella) and in varieties of Rumex; as ammonium salt in guano; as calcium salt in rhubarb root, in various lichens and in plant cells; as sodium salt in species of Salicornia and as free acid in varieties of Boletus.
Hooker enumerated twenty-one species of flowering plants, and seven of ferns, lycopods, and Characeae; at least seventyfour species of mosses, twenty-five of Hepaticae, and sixty-one of lichens are known, and there are probably many more.
On the summits of the Adirondacks are a few alpine species, such as reindeer moss and other lichens; on the shores of Long Island, Staten Island and Westchester county are a number of maritime species; and on Long Island are several species especially characteristic of the pine barrens of New Jersey.
The summits of some of the mountains are too high for trees and above belts of dwarf spruce, balsam and birch they are clothed chiefly with sandworts, diapensia, cassiope, rushes, sedges and lichens.
Its nest, which is a model of neatness and symmetry, it builds on trees and bushes, preferring such as are overgrown with moss and lichens.
The outside consists of moss and lichens, and according to Selby, "is always accordant with the particular colour of its situation."
Their food is entirely vegetable, especially grass roots and stalks, shoots of dwarf birch, reindeer lichens and mosses, in search of which they form, in winter, long galleries through the turf or under the snow.
Owing to their peculiar dual nature, lichens are able to live in situations where neither the alga nor fungus could exist alone.
The lichens are characterized by their excessively slow growth and their great length of life.
Until comparatively recent times the lichens were considered as a group of simple organisms on a level with algae and fungi.
In 1865 De Bary suggested the possibility that such lichens as Collema, Ephebe, &c., arose as a result of the attack of parasitic Ascomycetes upon the algae, Nostoc, Chroococcus, &c. In 1867 the observations of Famintzin and Baranetzky showed that the gonidia, in certain cases, were able to live outside the lichen-thallus, and in the case of Physcia, Evernia and Cladonia were able to form zoospores.
Although Schwendener supported this view of the " dual " nature of lichens by very strong evidence and identified the more common lichen-gonidia with known free-living algae, yet the theory was received with a storm of opposition by nearly all lichenologists.
He investigated the exact relation of fungus and alga and showed that the same alga is able to combine with a number of different fungi to form lichens; thus Chroolepns umbrinus is found as the gonidia of 13 different lichen genera.
The view of the dual nature of lichens had hitherto been based on analysis; the final proof of this view was now supplied by the actual synthesis of a lichen from fungal and algal constituents.
We can distinguish this class of forms as lichens with a homoiomerous thallus, i.e.
The soredia are found in a large number of lichens, and consist of a single gonidium or groups of gonidia, surrounded by a sheath and hyphae.
The soredia are the most successful method of reproduction in lichens, for not only are some forms nearly always without spore-formation and in others the spores laregly abortive, but in all cases the spore represents only the fungal component of the thallus, and its success in the development of a new lichen-thallus depends on the chance meeting, at the time of germination, with the appropriate algal component.
As the remarks on the nature of the spermatia show, the question of the sexuality of the lichens has been hotly disputed in common with that of the rest of the Ascomycetes.
In other lichens we should expect to find the ascogenous hyphae arising directly from the vegetative hyphae as in Humaria rutilans among the ordinary fungi, where the process is associated with the fusion of vegetative nuclei.
It is owing to the power of disintegrating by both mechanical and chemical means the rocks on which they are growing that lichens play such an important part in soil-production.
The resistance of lichens is extraordinary; they may be cooled to very low temperatures and heated to high temperatures without being killed.