Sporangia sentence example
In Peronospora, Saprolegnia, &c., the ends of the branches swell up into sporangia, which develop zoospores in their interior (zoosporangia), or their contents become oospheres, which may be fertilized by the contents of other branches (antheridia) and so form egg-cases (oogonia).
The same laws apply to the individual hyphae and their branches as to simple sporophores, and as long as the conidia, sporangia, gametes, &c., are borne on their external surfaces, it is quite consistent to speak of these as compound sporophores, &c., in the sense described, however complex they may become.
Mycelium well developed; sexual reproduction by zygospores; asexual reproduction by sporangia and conidia.
Klebs has shown that the development of zoosporangia or of oogonia and pollinodia respectively in Saprolegnia is dependent on the external conditions; so long as a continued stream of suitable food-material is ensured the mycelium grows on without forming reproductive organs, but directly the supplies of nitrogenous and carbonaceous food fall below a certain degree of concentration sporangia are developed.
They are characterized especially by the zygospores, but the asexual organs (sporangia) exhibit interesting series of changes, beginning with the typical sporangium of Mucor containing numerous endospores, passing to cases where, as in Thamnidium, these are accompanied with more numerous small sporangia (sporangioles) containing few spores, and thence to Chaetocladium and Piptocephalis, where the sporangioles form but one spore and fall and germinate as a whole; that is to say, the monosporous sporangium has become a conidium, and Brefeld regarded these and similar series of changes as explaining the relation of ascus to conidium in higher fungi.Advertisement
In addition to sporangia and the conidial spores referred to, some Mucorini show a peculiar mode of vegetative reproduction by means of gemmae or chlamydospores - i.e.
The classification of the Mucorini depends on the prevalence and characters of the conidia, and of the sporangia and zygospores - e.g.
In the formation of sporangia two cells fuse together by means of outgrowths, in a manner very similar to that of Spirogyra; sometimes, however, the wall between two cells merely breaks down.
The asexual cells are immotile spores arising in fours in sporangia from superficial cells of the thallus.
The possession of two kinds of reproductive organs, unilocular and plurilocular sporangia, is general among the rest of the Phaeosporeae.Advertisement
Bornet, however, called attention in 1871 to the fact that two kinds of plurilocular sporangia occurred in certain species of the genus Ectocarpus - somewhat transparent organs of an orange tint producing small zoospores, and also more opaque organs of a darker colour producing relatively larger zoospores.
Lebelii, together with the new species, into a genus, Giffordia, characterized by the possession of two kinds of plurilocular sporangia.
The conjugation of similar gametes, arising from distinct plurilocular sporangia, was observed by Berthold in Ectocarpus siliculosus and Scytosiphon lomentarius in 1880; and these observations have been recently confirmed in the case of the former species by Sauvageau, and in the case of the latter by Kuckuck.
In these cases, however, the potential gametes may, failing conjugation, germinate directly, like the zoospores derived from unilocular sporangia.
The assertion of Areschoug that conjugation occurs among zoospores derived from unilocular sporangia, in the case of Dictyosiphon hippuroides, is no doubt to be ascribed to error of observation.Advertisement
It would thus seem that the explanation of the existence of two kinds of sporangia, unilocular and plurilocular, among Phaeosporeae, lies in the fact that unilocular sporangia are for asexual reproduction, and that plurilocular sporangia are gametangia - potential or actual.
Moreover, for the important family of the Laminariaceae only unilocular sporangia are known to occur; and for many species of other families, only one or other kind, and in some cases neither kind, has hitherto been observed.
The sporangia may be terminal or intercalated.
When the threads reach the air they branch in a tree-like manner, and each branch (sporangiophore) carries one or more ovate sporangia, as shown at E, E, E, which fall off and are carried by the wind.
The sporangia may also germinate directly without undergoing division.Advertisement
The sporangia (pollen-sacs), which occur on the under-side of the stamens, are often arranged in more or less definite groups or sori, interspersed with hairs (paraphyses); dehiscence takes place along a line marked out by the occurrence of smaller and thinner-walled cells bounded by larger and thickerwalled elements, which form a fairly prominent cap-like " annulus " near the apex of the sporangium, not unlike the annulus characteristic of the Schizaeaceae among ferns.
The spores produced in each sporangium vary from very many to a single one in the case of some heterosporous forms. These latter bear spores of two kinds, microspores and megaspores, in separate sporangia.
D, E, Sporophylls bearing sporangia, which in E have opened.
There is a close resemblance between these sporangiophores and those of Equisetum, but as a rule only four sporangia were borne on each.
Some Calamites were heterosporous, sporangia with microspores and megaspores being found in the same cone.Advertisement
The overlapping bracts afforded protection to the sporangia, which were borne on sporangiophores springing from the upper surface of the coherent bracts near their origin from the axis; two sporangiophores usually arose from each bract, and sometimes adhered to its upper surface for some distance.
Each bent round at the upper end, and bore one or two sporangia on the side turned towards the axis.
In other species of Sphenophyllum, which are known only as impressions, single sporangia, or groups of four, appear to have been inserted directly on the upper surface of the bracts.
From each segment, near its base, a stalked peltate sporangiophore arose; this bore four sporangia, which hung parallel to the stalk.
The leaves, which bear the sporangia, are dichotomous, and do not form definite cones, but alternate in irregular zones with the foliage leaves.Advertisement
The sporangia of the Psilotaceae are associated in synangia, which occupy the same position relatively to the sporophyll, as the single sporangium of Lycopodium or the group of sporangia in Spenophyllum majus.
As general characteristics of the Lycopodiales, the simple form of the leaves, which are generally of small size, and the situation of the sporangia on the upper surface of the sporophylls, which are often associated in cones, close to their insertion on the axis, may be mentioned; there are both homosporous and heterosporous forms, the prothalli exhibiting corresponding differences.
The spores are formed in sporangia of considerable size, situated on the upper surface and near the base of the sporophylls.
The cavities of the large sporangia were sometimes traversed by trabeculae of sterile tissue resembling those found in Isoetes.
In some of the heterosporous forms (Lepidocarpon, Miadesmia) the sporangia were sometimes surrounded by an integument; and since only a single megaspore attained maturity, the structure of the megasporangium suggests a comparison with an ovule.Advertisement
The leaves have a single main bundle, and in the mesophyll are four longitudinal series of large intercellular spaces separated by transverse diaphragms. The sporangia, which are situated singly on the adaxial surface of the leaves, between their insertion on the stem and the ligule, arise from a considerable number of epidermal cells.
The spike is most simple in Ophioglossum, where it bears on each side a row of large sporangia, which hardly project from the surface, the vascular bundles occupying a central position.
In the young spike, which arises when the leaf is still very small, a band of tissue derived from superficial cells is distinguishable along either side; this sporangiogenic band gives rise to the sporogenous groups, the sterile septa between them, and the outer walls of the sporangia.
The spike of Helminthostachys corresponds to that of Ophioglossum, but in it the sporangia are borne on two lateral rows of branched sporangiophores.
The sporangia themselves resemble those of Botrychium, which project from the ultimate subdivisions of the branched spike; each is developed from a number of cells, the sporogenous tissue arising from a single cell.Advertisement
The older view was that it was a fertile segment of the leaf; and though its ventral position presents a difficulty, this must be regarded as a possible explanation; the occasional occurrence of sporangia on the lamina in Botrychium has been regarded as supporting it.
The sporangia are borne in groups (sori) on the under surface of the leaves; sometimes the fertile leaves differ more or less from the purely vegetative ones.
In some apogamous Ferns sporangia may occur on the prothallus and the vegetative organs of the sporophyte may also occur singly.
In a number of cases, though not in all, apospory appears to be correlated with a failure of the sporangia to develop.
The large sporangia, each of which originates from a number of superficial cells, are here incompletely separated from one another and arranged in a single circle forming a synangium.Advertisement
In Todea the sori, each of which consists of a single circle of bulky sporangia, are borne on the under surface of the pinnae.
In Osmunda the region of the leaf which bears the sporangia has its lamina little developed; the leaf thus bears sterile and fertile pinnae, or, as in 0.
The sporangia originate from single cells, though surrounding cells may contribute to the formation of the stalk.
The sporangia are borne singly or in sori of two or three on the margin or under surface of leaves, the fertile pinnae of which differ more or less from the sterile segments.
The sporangia arise simultaneously in the sorus, which is borne on the under surface of the ordinary pinna; in those species with large sporangia the latter form a single circle, in others sporangia may also arise from the central part of the receptacle.Advertisement
The sporangia, which arise in basipetal succession on the receptacle, dehisce by a median slit, though the annulus is somewhat oblique; they have resemblances to the Gleicheniaceae.
When mature, the sporangia are raised above the margin of the indusium by the elongation of the receptacle, thus facilitating the dispersion of the spores.
The sori, which are marginal, have a long receptacle, bearing the sporangia in basipetal succession, and are surrounded by a cup-shaped indusium.
The sporangia present a considerable range in size, the largest being found in species of Hymenophyllum, the smallest in Trichomanes.
The sorus has a somewhat elongated receptacle, on which the sporangia arise basipetally; the indusium may be cup-shaped, bivalve or wanting.
The sporangia dehisce by a transverse slit, the annulus being truly vertical or, in some of the genera in which they are regularly arranged, very slightly oblique.
A consideration of the Filicaceae as arranged above will show that the several sub-orders may in general terms be said to form a series between those in which the sorus consists of a single circle of bulky sporangia and those Polypodiaceae in which the numerous small sporangia appear to be grouped without order in the sorus.
When the survey is extended to the extinct Ferns of which the fructification is known, many of those from the more ancient rocks are found to group themselves with the existing sub-orders with large sporangia, such as the Marattiaceae, Gleicheniaceae and Schizaeaceae; the Polypodiaceae, on the other hand, do not appear until much later.
The extinct forms cannot be dealt with in detail here; but it may be pointed out that their order of appearance affords a certain amount of direct evidence that the existing Ferns with a single circle of large sporangia in the sorus are relatively primitive.
On the ground mainly of an examination of the sorus and sporangium, Bower has shown that the Filicaceae may be divided into three groups - the Simplices, Gradatae and Mixtae - in which the sporangia arise simultaneously, in basipetal succession, or irregularly in the sorus respectively.
The differences in the form and mode of dehiscence of the sporangia (those of the Simplices having median dehiscence and a horizontal annulus, those of the Gradatae a more or less oblique position of the annulus and of the plane of dehiscence, while in the Mixtae the annulus is vertical and the dehiscence transverse) stand in relation to the position of the sporangia in the sorus relatively to one another.
The absence of an annulus from their indehiscent sporangia makes it impossible to compare them with the other Ferns in respect of this important character.
The sporangia in both genera are associated in sori enclosed by indusia springing from the base of the receptacle.
While a number of ferns can be multiplied vegetatively, by buds formed on the leaves and in other ways, the regular mode of propagation is by sowing the spores shed from the ripe sporangia.
If sporangia and spores are present they also may persist in a perfectly recognizable form, and in fact much of our knowledge of the fructification of fossil Ferns and similar plants has been derived from specimens of this kind.
A minute Fungus bearing sporangia, found by Renault in the wood of a Lepidodendron, and named by him Oiichytrium Lepidodendri, is referred with much probability to the Chytridineae.
The sporangiophores, which are usually half as numerous in each verticil as the bracts, have the same form as in Equisetum, but each bears four sporangia only.
Diagrammatic longitudinal section of cone, showing the axis (ax) bearing the bracts (br) with peltate sporangiophores (sp) springing from their axils; sm, sporangia.
Part of cone, showing the axis (ax) bearing peltate sporangiophores (sp) without bracts; sm, sporangia.
Diagrammatic longitudinal section of the cone, showing the axis (ax) bearing alternate whorls of bracts (br) and peltate sporangiophores (sp) with their sporangia (sm).
Dawsoni in the fact that each sporangiophore bears two sporangia, attached to a distal expansion approaching the peltate scale of the Equisetales.
In Sphenophyllum majus, where the cones are less sharply defined, the forked bract bears a group of four sporangia at the bifurcations, but their mode of insertion has not yet been made out.
The dorsal segments are sterile, corresponding to the bracts of Sphenophyllum Dawsoni, while the ventral segments constitute peltate sporangiophores, each bearing four sporangia, just as in a ax FIG.
While the anatomy has a somewhat Lycopodiaceous character, the arrangement of the appendages is altogether that of the Sphenophylleae; at the same time Calamarian affinities are indicated by the characters of the sporangiophores and sporangia.
Among existing plants their nearest affinities would appear to be with Psiloteae, as indicated not merely by the anatomy, but much more strongly by the way in which the sporangia are borne.
There is good reason to believe that the ventral synangium of the Psiloteae corresponds to the ventral sporangiophore with its sporangia in the Sphenophyllales.
The fructification consists of long, lax spikes, with whorled sporophylls; indications of megaspores have been detected in the sporangia.
The fructifications by themselves are not necessarily decisive, for in certain cases the supposed sporangia of Marattiaceous Ferns have turned out to be in reality the microsporangia or pollen-sacs of seed-bearing plants (Pteridosperms).
Typically Marattiaceous sori, consisting of exannulate sporangia united to form synangia, are frequent, and are almost always found on fronds with the character of Pecopteris, large, repeatedly pinnate leaves, resembling those of Cyatheaceae or some species of Nephrodium.
In Ptychocarpus the fusion of the sporangia to form the synangium was much more complete; Scolecopteris resembles A sterotheca, but each synangium is stalked.
In the Grand' Eurya of Stur the sporangia appear to have been free from each other, as in Angiopteris.
Group of annulate sporangia, magnified.
The sporangia were large pyriform sacs, shortly stalked, and borne in tufts on the branches of the fertile rachis, which developed no lamina.
On the fertile rachis the sporangia were borne in tufts, much as in the preceding genus; they were still larger, reaching 2.5 mm.
The genus Corynepteris of Baily is interesting from the fact that its sporangia, while individually similar to those of Zygopteris, were grouped in sori or synangia, resembling those of an Asterotheca.
Fertile leaflets, day, while fern like in habit bearing sporangia, and sterile, were Cycadean in structure.
It is only recently that undoubted sporangia have been found in close association with Glossopteris leaves.
The abundance of Palaeozoic plants with sporangia and sori of the Marattiaceous type is in striking contrast to the scarcity of Mesozoic ferns which can be reasonably included in the Marattiaceae.
This Jurassic species bore bipinnate fronds not unlike those of the South African, Australian, and New Zealand Fern Todea barbara, which were characterized by a stout rachis and short broad pinnules bearing numerous large sporangia covering the under surface of the lamina.
Specimens of Todites have been obtained from England, Poland, and elsewhere, sufficiently well preserved to afford good evidence of a correspondence in the structure of their sporangia with those of recent Osmundaceae.
Ctenis has been incorrectly placed among the ferns by some authors, on account of the occurrence of supposed sporangia on its pinnae; but there is reason to believe that these so-called sporangia are probably nothing more than prominent papillose cells of the epidermis.
Numerous semi-papillate, deciduous, sympodial sporangia were observed in addition to hyaline to light brown, large chlamydospores.
Sporangia Sporangia are the airborne spores of the blight pathogen and are responsible for the rapid spread of the disease in crops.
At maturity, the protoplasts convert to sporangia, which release zoospores into the soil.
Some shoots are sterile while others are fertile, bearing at the apex the so-called fructification - a dense oval, oblong conical or cylindrical spike, consisting of a number of shortly-stalked peltate scales, each of which has attached to its under surface a circle of spore-cases (sporangia) which open by a longitudinal slit on their inner side.
Klebs has concluded that transpiration is the important factor in determining the formation of sporangia, while zygotedevelopment depends on totally different conditions; these results have been called in question by Falck.
The mycelium from the germinating sporangia or zoospores soon finds its way into the tissues of the potato leaf by the organs of transpiration, and the process of growth already described is repeated -over and over again till the entire potato leaf, or indeed the whole plant, is reduced to putridity.
The great majority of ferns have sporangia that are stalked capsules with walls only one cell thick.
This had a hyaline mycelium bearing lemon-shaped sporangia which released motile zoospores after chilling in water, consistent with P. infestans.
Two different types of asexual ' spores ' called sporangia and chlamydospores are formed.
Soil surveys were carried out in the affected areas revealed that resting sporangia were detected.
Fig 2. Part of a blade of grass, about 4 mm diameter, covered with small sporangia of the slime mold Physarum cinereum.
A, Fertile shoot, springing B, C, Sporophylls bearing sporangia, from the rhizome, which which in C have opened.