In France mushroom-growers do not use the compact blocks or bricks of spawn so familiar in England, but much smaller flakes or "leaves" of dry dung in which the spawn or mycelium can be seen to exist.
The common mushroom (Agaricus campestris) is propagated by spores, the fine black dust seen to be thrown off when a mature specimen is laid on white paper or a white dish; these give rise to what is known as the "spawn" or mycelium, which consists of whitish threads permeating dried dung or similar substances, and which, when planted in a proper medium, runs through the mass, and eventually develops the fructification known as the mushroom.
This spawn may be obtained from old pastures, or decayed mushroom beds, and is purchased from nurserymen in the form of bricks charged with the mycelium, and technically known as mushroom spawn.
A characteristic feature of the fungal vegetative plantbody (mycelium) is its formation from independent coenocytic tubes or cell-threads.
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.
The formation of a massive body naturally involves the localization of the absorptive region, and the function of absorption (which in the simpler forms is carried out by the whole of the vegetative part of the mycelium penetrating a solid or immersed in a liquid substratum) is subserved by the outgrowth of the hyphae of the surface-layer of that region into rhizoids, which, like those of the Algae living on soil, resemble the root-hairs of the higher plants.
Some make their way through the cells of the outer part of the cortex towards the root-tip, and form a mycelium or feltwork of hyphae, which generally occupies two or three layers of cells.
This wood is in great part already dead substance, but the mycelium gradually invades the vessels occupied with the transmission of water up the trunk, cuts off the current, and so kills the tree; in other cases such Fungi attack the roots, and so induce rot and starvation of oxygen, resulting in fouling.
The extraordinary malformations known as Witches Brooms, caused by the repeated branching and tufting of twigs in which the mycelium of Exoascus (on birch) or Aecidium (on silver fir) are living, may be borne in considerable ntimbers for years without any very extensive apparent injury to the tree.
White or grey spots may be due to Peronospora, Erysiphe, Cystopus, Entyloma and other Fungi, the mycelium of which will be detected in the discoloured area; or they may be scale insects, or the results of punctures by Red-spider, &c. Yellow spots, and especially bright orange spots, commonly indicate Rust Fungi or other Uredineae; but Phyllosticta, Exoascus, Clasterosporium, Synchytrium, &c., also induce similar symptoms. Certain Aphides, Red-spider, Phylloxera and other insects also betray their presence by such spots.
The fungus mycelium grows between the cuticle and the epidermis, the former being ultimately ruptured by numerous short branches bearing spores (conidia) by means of which the disease is spread.
Portion of the mycelium of the fungus bearing spores (conidia), s, on erect branches, X250.
The disease is characterized by the appearance of a mycelium forming white or greyish-white patches on the young leaves; this spreads quickly and attacks the older leaves and branches, and ultimately reaches the grapes.
The disease spreads by the mycelium growing ever the epidermis of the plant.
A and B, mycelium (m), the mix t ure over the affe c ted with haustoria (h).
The mycelium spreads through the green parts of the plant, attacking the leaves, twigs and unripe grapes.
The mycelium of Sphaceloma grows just beneath the cuticle of the vine, through which it soon bursts, giving rise to a number of minute hyphae, which bear conidia.
Mycelium of the fungus attacking root of vine (reduced).
The hyphae of the mycelium of this fungus are septate, with numerous short branches.
6), which forms subterranean strings of mycelium - so-called rhizomorphs.
The wood is nearly white, or of a yellowish tint, but sometimes exhibits blackish markings due to the mycelium of a fungus.
The mycelium produced from the spores dropped by the fungus or from the "spawn" in the soil, radiates outwards, and each year's successive crop of fungi rises from the new growth round the circle.
This prevents infection from outside and also destroys any spores or fungus mycelium that may have been packed away along with the bulbs.
The fungus-mycelium will go on growing indefinitely in the cambium layer, thus killing and destroying a larger area year by year.
By the fusion of the hyphae in the middle of the mycelium a pseudo-parenchymatous cortical layer has begun to form.
It any state most plants feed greedily upon it, and when pure or free from decaying wood or sticks it is a very safe ingredient in composts; but it is so liable to generate fungus, and the mycelium or spawn of certain fungi is so injurious to the roots of trees, attacking them if at all sickly or weakened by drought, that many cultivators prefer not' to mix leaf-mould with the soil used for permanent plants, as peaches or choice ornamental trees.
A widespread disease known as pocket-plums or bladderplums is due to an ascomycetous fungus, Exoascus pruni, the mycelium of which lives parasitically in the tissues of the host plant, passes into the ovary of the flower and causes the characteristic malformation of the fruit which becomes a deformed, sometimes curved or flattened, wrinkled dry structure, with a hollow occupying the place of the stone; the bladder plums are yellow at first, subsequently dingy red.
Mycelium with haustoria (h); 2, Erysiphe; A and B, mycelium (m), with haustoria (h).
Mycelium with haustoria (h); 2, Erysiphe; A and B, mycelium (m), with haustoria (h).
In Arthrobotrys side-branches of the mycelium sling themselves around the host (Tylenchus) much as tendrils round a support.
As a rule the nuclei of the mycelium are very minute (1.5-2 µ in Phycomyces), but those of many asci and spores are large and easily rendered visible.
Much more complicated are the processes in a large series of "fructifications," where the mycelium first develops a densely packed mass of hyphae, all alike, in which labyrinths of cavities subsequently form by separation of hyphae in the previously homogeneous mass, and the hymenium covers the walls of these cavities and passages as with a lining layer.
Mycelium usually well developed, but sometimes poor or absent.
Mycelium present, antheridia with antherozoids, oogonium with single oosphere: Monoblepharidaceae.
Mycelium present; antheridia but no antherozoids; oogonia with one or more oospheres: Peronosporaceae, Saprolegniaceae.
Mycelium poorly developed or absent; oogonia and antheridia (without antherozoids) known in some cases; zoospores common: Chytridiaceae.
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.
This explains the sequence of events in the case of a Saprolegnia-mycelium radiating from a dead fly in water.
Those parts nearest the fly and best supplied develop barren hyphae only; in a zone at the periphery, where the products of putrefaction dissolved in the water form a dilute but easily accessible supply, the zoosporangia are developed in abundance; oogonia, however, are only formed in the depths of this radiating mycelium, where the supplies of available food materials are least abundant.
These parasitic and minute, chiefly aquatic, forms may be looked upon as degenerate Oomycetes, since a sexual process and feeble unicellular mycelium occur in some; or they may be regarded as series of primitive forms leading up to higher members.
In the first group zygospores can arise by the union of branches from the same mycelium and so can be produced by the growth from a single spore; this group includes Spordinia grandis, Spinellus fusiger, some species of Mucor, &c. The majority of forms, however, fall into the heterothallic group, in which the association of branches from two mycelia different in I nature is necessary for the 2, formation of zygospores.