How to use Thallus in a sentence
The Mosses and Liverworts include forms with a more or less leaf-like thallus, such as many of the liverworts, and forms in which the plant shows a differentiation into a stem bearing remarkably simple leaves, as in the true mosses.
This process may result in a considerable thickening of the thallus.
Thallophyta are the most lowly organized plants and include a great variety of forms, the vegetative portion of which consists of a single cell or a number of cells forming a more or less branched thallus.
The thallus in all cases consists of a branched filament of cells placed end to end, as in many of the Green Algae.
Or the thallus may have a leaf-like form, the branches from the central threads which form the midrib growing out mainly in one plane and forming a lamina, extended right and left of the midrib.Advertisement
In many Laminariaceae the thallus also grows regularly in thickness by division of its surface layer, adding to the subjacent permanent tissue and thus forming a secondary meristem.
In the Bryophytes water is still absorbed, not only from the soil but also largely from rain, dew, &c., through the general surface of the subaerial body (thallus), or in the more differentiated forms through the leaves.
A sufficient description of the thallus of the liverworts will be found in the article BRYOIHYTA.
The frondose (thalloid) Jungermanniales show no such differentiation of an assimilating tissue, though the upper cells of the thallus usually have more chlorophyll than the rest.
They serve to conduct water through the thallus, the assimilating parts of which are in these forms often raised above the soil and are comparatively remote from the rhizoid-bearing (water-absorbing) region.Advertisement
In the liverworts we find fixation of the thallus by water-absorbing rhizoids; in certain forms with a localized region of water-absorption the development of a primitive hydrom or water-conducting system; and in others with rather a massive type of thallus the differentiation of a special assimilative and transpiring system.
The gametophyte, which bears the sexual organs, is either a free-living thallus corresponding in degree of differentiation with the lower liverworts, or it is a mass of cells which always remains enclosed in a spore and is parasitic upon the sporophyte.
From the primitive uniform Systems. mass of undifferentiated assimilating cells, which we may conceive of as the starting-point of differentiation, though such an undifferentiated body is only actually realized in the thallus of the lower Algae, there is, (1) on the one hand, a specialization of a surface layer regulating the immediate relations of the plant with its surroundings.
In mounting collemas it is advisable to let the specimen become dry and hard, and then to separate a portion from adherent mosses, earth, &c., and mount it separately so as to show the branching of the thallus.
The green (or blue-green) cells were termed gonidia by Wallroth, who looked upon them as asexual reproductive cells, but when it was later realized that they were not reproductive elements they were considered as mere outgrowths of the hyphae of the thallus which had developed chlorophyll.Advertisement
Rees in 1871 produced the sterile thallus of a Collema from its constituents; later Stahl did the same for three species.
The thallus or body of the lichen is of very different form in different genera.
We can distinguish this class of forms as lichens with a homoiomerous thallus, i.e.
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.
In external form the heteromerous thallus presents the following modifications.Advertisement
I, Germinating ascospore (sp) 2, Thallus in process of formawith branching germ-tube tion.
In colour also the thallus externally is very variable.
The surface of the thallus often exhibits outgrowths in the form of warts, hairs, &c. The medullary layer, which usually forms the main part of the thallus, is distinguished from the cortical layer by its looser consistence and the presence in it of numerous, large, air-containing spaces.
These structures are known as cephalodia and they usually occupy a definite position in the thallus.
They are distinguished by possessing as gonidia algae foreign to the ordinary part of the thallus.Advertisement
In the first process, portions of thallus containing gonidia may be accidentally separated and so may start new plants.
Since they are provided with both fungal and algal elements, they are able to develop directly, under suitable conditions, into a new thallus.
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.
In the other view the spermatia are the male sexual cells and thus A, Optical longitudinal section of the ex are rightly named; it tremity of a thin branch of the thallus should, however, be which has become transparent in pointed out that this solution of potash.
In favour of the conidial view is the fact that in the case of Collema and a few other forms the spermatia have been made to germinate in artificial cultures, and in the case of Calicium parietinum Moller succeeded in producing a spermogonia bearing thallus from a spermatium.Advertisement
For the germination of the spermatia in nature there is only the observation of Hedlund, that in Catillaria denigrata and C. prasena a thallus may be derived from the spermatia under natural conditions.
The apothecia, though of the normal fungal type and usually disk-shaped, are somewhat more variable, and since the Morphologie and Biologie der Pilze, Mycetozoen und 1 The thalline margin (margo thallinus) is the projecting edge of a special layer of thallus, the amphithecium, round the actual apothecium; the proper margin (margo proprius) is the projecting edge of the apothecium itself.
He showed that the archicarp consisted of two parts, a lower coiled portion, the ascogonium, and an upper portion, the trichogyne, which projected from the thallus.
When the spores germinate the germ-tubes surround the algal cells, which now increase in size and become the normal gonidia of the thallus.
Clavaria mucida, however, h a s apparently some claims to be considered as a Basidiolichen, since the base of the fruit body and the thallus from which it arises, according to Coker, always shows a mixture of hyphae and algae.Advertisement
When the fungus predominates in the thallus it has a bracket-like mode of growth and is found projecting from the branches of trees with the hymenium on the under side.
A solution of iodine is also used as a test owing to the blue or wine-red colour which the thallus, hymenium or spores may give with this reagent.
Most systems agree in deriving the major divisions from the characters of the reproductive organs (perithecia, apothecia, or basidiospore bearing fructification), while the characters of the algal cells and those of the thallus generally are used for the minor divisions.
Fungi with segmental thallus; sexual reproduction sometimes with typical antheridia and oogonia (ascogonia) but usually much reduced.
Forms with septate thallus, and reproduction by chlamydospores which on germination produce sporidia; sexuality doubtful.Advertisement
Thallus septate; spores developed in special type of sporangium, the ascus, the number of spores being usually eight.
Amongst the lower plants, however, it is found that a demarcation into stem and leaf is impossible, but that there is a structure which partakes of the characters of both - such is a thallus.
Certain species are regularly found in the intercellular spaces of higher plants; such are species of Nostoc in the thallus of Anthoceros, the leaves of Azolla and the roots of Cycads.
The thallus may be unicellular or multicellular.
Valoniaceae and The thallus is of more varied structure in this group than in any Dasycladaceae are partially septate, but elsewhere no cellulose partiother.Advertisement
In the simplest case it may consist of a single cell, which may tions occur, and the thallus is more or less the continuous tube from remain free during the whole of the greater part of its t xistence, which the group is named.
The Ulvaceae, the thallus of which consists of external form as an expanded Coprinus, Neomeris simulates the laminae, one or more cells thick, or hollow tubes, probably represent fertile shoot of Equisetum with its densely packed whorled branches, a still more advanced stage in the passage of a colony into a multiand in Microdictyon, Anadyomene, Struvea and Boodlea the branches, cellular plant.
Attached to the bottom of pools series of the Confervales, the thallus consists of filaments branched by means of rhizoids, the thallus of Characeae grows upwards by or unbranched, attached at one extremity, and growing almost means of an apical cell, giving off whorled appendages at regular wholly at the free end.
There is thus a Protococcales, and in the bulk of the Confervales, the thallus consists close approach to the external morphology of the higher plants.
Valonia and Caulerpa among Siphonales detach portions of their thallus, which are capable of independent growth.Advertisement
In unicellular forms (Sphaerella) the thallus becomes transformed into a zoosporangium at the reproductive stage.
Indeed the genus Oedogonium exhibits a high degree of specialization in its reproductive system, considering that its thallus has not advanced beyond the stage of an unbranched filament.
Akinetes are ordinary thallus cells, which on account of their acquisition of a thick wall are capable of surviving unfavourable conditions.
In Fucaceae, Dictyotacea, and in Laminariaceae and Sphacelariaceae, among Phaeosporeae, the thallus consists of a true parenchyma; elsewhere it consists of free filaments, or filaments so compacted together, as in Cutleriaceae and Desmarestiaceae, as to form a false parenchyma.
In Laminariaceae secondary cylindrical props arise obliquely from the base of the thallus.
In Fucus vesiculosus they arise in lateral pairs; in Ascophyllum they are single and median; in Macrocystis one vesicle arises at the base of each thallus segment; in Sargassum and Halidrys the vesicles arise on special branches.
In Fucaceae an apical cell is situate at the surface of the thallus in a slit-like depression at the apex.
In Desmarestia and Arthrocladia, for example, it is found that the thallus ends in a tuft of such hairs, each of them growing by means of an intercalated growing point.
In Cutleria the laminated thallus is formed in the same way.
While the laminated portion of the thallus is being gradually worn off in our latitudes during the autumnal storms, a vigorous new growth appears at the junction of the stipe and the blade, as the result of which a new piece is added to the stipe and the lamina entirely renovated.
The sexual organs - oogonia and antheridia - are borne on special portions of the thallus in cavities known as conceptacles.
The asexual cells are immotile spores arising in fours in sporangia from superficial cells of the thallus.
The thallus is somewhat spherical and unicellular, exhibiting a distinction between anterior and posterior extremities, and dorsal and ventral surfaces.
Cutleria sp., margin of thallus showing trichothallic growth.
Like the Fungi, therefore, the Red Algae consist for the most part of branched filaments, even where the thallus appears massive to the eye, and, as in the case of Fungi, this fact is not inconsistent with a great variety of external morphology.
In the great majority the thallus is obviously filamentous, as in some species of Callithamnion.
The branching of the thallus, which meets the eye in all these cases, is due to the unlimited growth of a few branches.
In Iridaea the thallus is an entire lamina; in Callophyllis a lobed lamina; in Delesseria it is provided with midrib and veins, simulating the appearance of a leaf of the higher plants; in Constantinea the axis remains cylindrical, and the lateral branches assume the form of leaves.
Melobesia callithamnioides gives rise to multicellular propagula; Griffithsia corallina is said to give rise to new individuals, by detaching portions of the thallus from the base of which new attachment organs have already arisen.
The ventral portion of the carpogonium may be imbedded deep in the thallus in the massive species; the trichogyne, however, always reaches the surface.
When the cystocarps or segments of cystocarps are formed in the substance of a thallus, the site is marked merely by a swelling of the substance.
The attachment of the cell of an ooblastema filament to a cell of the thallus may be effected by means of a minute pore, or the two cells may fuse their contents into one protoplasmic mass.
It is possible, however, that the tetraspore formation should be regarded as comparable with the prolific vegetative reproduction of Bryophyta, and in favour of this view there is the fact that the tetraspores originate on the thallus in a different way from carpospores with which the spores of Bryophyta are in the first place to be compared; moreover, in certain Nemalionales the production of tetraspores does not occur, and the difficulty referred to does not arise in such cases.
He finds that eight chromosomes appear in karyokinesis in the ordinary thallus cells, but sixteen in the gonimoblast filaments derived from the fertilized carpogonium.
In Sphaeroplea it is only at this stage that zoospores are formed at all; but in most cases, such as Oedogonium, Ulothrix, Coleochaete, similar zoospores are produced again and again upon the thallus, and the product of the oospore may be regarded as merely a first brood of a series.
Excepting where the thallus is impregnated with silica, as in Diatomaceae, or carbonate of lime, as in Corallinaceae,Characeae and some Siphonales, it is perhaps not surprising that algae should not have been extensively preserved in the fossil form.
There appears to be no reason to doubt that the sexual generation is homologous with the thallus of a Liverwort, or of such an Alga as Coleochaete.
It consists of minute interwoven tubular filaments, and has been variously interpreted as possibly representing the sheaths of a Cyanophycean Alga, and as constituting a Siphoneous thallus of the type of the Codieae.
The non-cellular order Siphoneae is fairly well represented in Palaeozoic strata, especially by calcareous verticillate forms referable to the family Dasycladeae; the separate tubular joints of the articulated thallus, bearing the prints of the whorled branches, are sometimes cylindrical (Arthroporella, Vermiporella, &c.), sometimes oval (Sycidium) or spherical (Cyclocrinus).
The boghead of Scotland, Autun and New South Wales is regarded by Renault and Bertrand as mainly composed of gelatinous Algae (Piles and Reinschia), having a hollow, saccate thallus formed of a single layer of cells.
It has recently been stated, however, that the supposed Algae are in reality the megaspores of Vascular Cryptogams. Scarcely anything is known of Palaeozoic Florideae; Solenopora, ranging from the Ordovician to the Jurassic, resembles, in the structure of its thallus, with definite zones of growth, Corallinaceae such as Lithothamnion, and may probably be of the same nature.
In one case the spherical thallus was found seated in a cup-like receptacle.
In the Lower Carboniferous of Scotland Mr Kidston has found several specimens of a large dichotomous thallus, with a very distinct midrib; the specimens, referred to the provisional genus Thallites, much resemble the larger thalloid Liverworts.
These fossil Hepaticae are unfortunately founded only on sterile fragments, and placed in the Liverworts on the strength of their resemblance to the thallus of Marchantia and other recent genera.
Most bryophytes have erect or creeping stems and tiny leaves, but hornworts and some liverworts have only a flat thallus and no leaves.
The dry lichen thallus is brittle, so fragments can be broken off easily and transported by wind or by animals.
The Mosses and Liverworts (see BRYOPHYTA) include forms with a more or less leaf-like thallus, such as many of the liverworts, and forms in which the plant shows a differentiation into a stem bearing remarkably simple leaves, as in the true mosses.
In a few of the lower forms (Sphacelariaceae), and in the, higher forms which possess a solid thallus, often of very large size, the plant-body is no longer formed entirely of branched cell-threads, but consists of what is called a true parenchymatous tissue, i.e.
The plant-body (thallus) is always small and normally lives in very damp air, so that the demands of terrestrial life are at a minimum.
We may note the universal Li occurrence on the lower surface of the thallus of fixing ver and absorbing rhizoids in accordance with the terrestrial Worts.
The Marchantiaceae (see article BRYOPHYTA) show considerable tissue-differentiation, possessing a distinct assimilative system of cells, consisting of branched cell threads packed with chloroplasts and arising from the basal cells of large cavities in the upper part of the thallus.
Ephebe pubescens) the form of thallus is the form of the filamentous alga which is merely surrounded by the fungal hyphae (fig.
D, Part of branched filamentous thallus of the multicellular Green Alga Oedocladium.
In the bulky forms colorless branches frequently grow out from some of the cortical cells, and, pushing among the already-formed threads in a longitudinal direction, serve to strengthen the thallus by weaving its original threads together.
Many of the lower forms of Brown Seaweeds (Phoeophyceae) have a thallus consisting of simple or branched cell threads, as in the green and red forms. The lateral union of the branches to form a solid thallus is not, however, so common, nor is it carried to so high a pitch of elaboration as in the Rhodophyceae.
In the Fucaceae, on the other hand, there is a single prismatic apical cell situated at the bottom of a groove at the growing apex of the thallus, which cuts off cells from its sides to add to the peripheral, and from its base to add to the central permanent cells.