Eugenius Warming

“ The wind also very easily conveys the conidia to healthy Potato-fields and infects them. The enormous quantity of conidia and swarm-cells that may be formed in the course of a summer explains the rapid spreading of the disease; and the preceding makes it clear why wet summers are favourable to its existence. When the swarm-cells germinate, they round off, and then surround themselves with a cell-wall which grows out into the germ-tube, and pierces through the epidermis of the host-plant (Fig. 92) . Having entered the host, a new mycelium is formed. ”

“ On the germination of the seed either the entire cotyledon, or its apex only, most generally remains in the seed and absorbs the nutritive-tissue, while the lower portion elongates and pushes out the plumule and radicle, which then proceed with their further growth. The primary root in most cases soon ceases to grow, but at the same time, however, numerous lateral roots break out from the stem, and become as vigorous as the primary root, or even more so. ”

“ The alternation of generations is as distinct in this Division as in the Mosses, but the sexual generation consists of only a small thallus, the prothallium, which bears directly the sexual organs, antheridia and archegonia; and the asexual generation, which arises from the fertilisation of the oosphere, is no longer a single short-lived sporangium, but a highly developed, generally perennial, plant provided with stem, leaves and true roots (Ferns, Horsetails, etc.) , the sporangia being borne on the leaves. ”

“ The reason for this is that systematic classifications must be based upon the relationship of form, development, and reproduction, and from this point of view we must regard the Bacteria as being the nearer relatives of the Blue-green Algæ. All the Thallophytes, which are designated Fungi (when the entire group of Slime-Fungi is left out) , form in some measure a connected series of development which only in the lower forms (Phycomycetes) is related to the Algæ, and probably through them has taken its origin from the Algæ; the higher Fungi have then developed independently from this beginning. ”

“ The pollen-grains are “multicellular,” i.e. there is always in their interior a distinct prothallium, formed by 1–3 cells, and a larger cell which gives rise to the pollen-tube.
Division 5. Angiospermæ. The carpels surround the ovules and form an entirely closed chamber (ovary) , in which the ovules mature and ripen into seeds. The surface of a portion of the apex of the carpel is transformed into the “stigma,” which, by a sticky fluid and also by hair-structures, is capable of retaining the pollen-grains conveyed to it by the wind, or more frequently by insects. ”

“ The embryo is forced more or less into the endosperm [247] in which it may rest for a longer or shorter time, and generally is developed to such an extent that it has a distinct primary-root (radicle) and stem (plumule) with one or more embryo-leaves (cotyledons) .
When the oosphere has been fertilised its nucleus sinks down to its lower end, and by repeated division into two, forms four cells lying in one plane (Fig. 253, see base of the left archegonium) . ”

“ The lowest Mosses have, however, a thallus. Fertilisation is accomplished by means of self-motile, spirally coiled spermatozoids, through the agency of water. From the fertilised oosphere a “fruit-body” (capsule) with unicellular organs of reproduction (spores) is produced. The spore on germination gives rise to the vegetative system, which bears the organs of sexual reproduction; and this system is divided into two stages—the protonema, and the leaf-bearing plant produced on it. ”

“ The oogonia are developed at the extremities of certain branches: they are bottle-shaped cells with very long and thin necks (trichogyne) , open at the end (a in A) ; at the base of each oogonium is a spherical oosphere. The spermatozoids reach the oosphere through the trichogyne, or through an aperture in the wall when the trichogyne is absent, and fertilisation having taken place, the oogonium becomes surrounded by a cell-layer (envelope) , which grows out from the cells near its base (b in A) , and in this way a kind of fruit is formed (B) (spermocarp, cystocarp) . ”

“ Contagion may take place both by introduction into wounds, and from the mucous membrane of the intestines or lungs, both by vegetative cells and by spores; in intestinal anthrax, however, only by spores. The Bacillus multiplies as soon as it has entered the blood, and the anthrax disease commences. The Bacilli not only give off poison, [40] but also deprive the blood of its oxygen. Vegetative cells only occur in living animals. This species is a facultative parasite which in the first stage is a saprophyte, and only in this condition forms spores. ”

“ The Wheat flowers at any time of the day, each flower lasting only a quarter of an hour. The pales open suddenly, but only half way, and the anthers scatter one-third of the pollen in their own flower and two-thirds outside. Self-pollination is effectual, but crossing gives better results. ”

“ The reproduction takes place as far as is known at present, only by division. This, in many salt water forms, may take place in the swarming condition, and, in that case, is always parallel to the longitudinal axis. The daughter-individuals, each of which retains half of the original shell, sometimes do not separate at once from each other, and thus chains (e.g. in Ceratium) of several connected individuals may be formed. In others, the division occurs after the cilia have been thrown off and the cell-contents rounded. The daughter-cells then adopt entirely new cell-walls. ”

“ The Sileneæ are as a rule adapted for pollination by insects with long probosces—especially butterflies,—and they are frequently protandrous, so that at first the calyx-stamens open, later on the corolla-stamens, then the stigmas expand. The honey is secreted by a ring-like nectary round the base of the ovary or by nectaries at the base of the stamens. Some only blossom and emit scent at night or in the evening (Lychnis vespertina, Silene nutans, Saponaria officinalis) and, like other night-flowers, are of a white or pale colour. ”

“ Sclerotia only occur in the higher Fungi, and are found both in saprophytes, e.g. Coprinus, and in parasites, e.g. Claviceps (Ergot) , Sclerotinia.
Reproduction. Sexual reproduction is found only among the lower Fungi which stand near to the Algæ, the Algal-Fungi, and takes place by the same two methods as in the Algæ, namely by conjugation and by the fertilisation of the egg-cell in the oogonium.
The majority of Fungi have only ASEXUAL reproduction. The most important methods of this kind of reproduction are the sporangio-fructification and the conidio-fructification. ”

“ The sexual generation. In the MICROSPORES are formed: (1) a very small “vegetative” cell, representing the vegetative part of the prothallium (f in Fig. 233 A, B) , and (2) a cell many times larger and which divides into a number (4–8) of primordial cells, each of which divides into four spermatozoid-mother-cells, though all of these may not develope spermatozoids. On germination, when the spore-wall is ruptured, the spermatozoids and spermatozoid-mother-cells are ejected into the water.
The SPERMATOZOIDS in Selaginella are elongated and club-shaped, with two cilia (Fig. 234) ”

“ The leaves are scattered, large, often deeply divided, and of various highly developed forms. The undeveloped leaves are rolled up in the bud, having what is termed circinate venation. The sporangia are situated on the edge or on the lower side of the leaves, those on which the sporangia are borne (sporophylls) being often the ordinary foliage-leaves; but in a few cases the fertile differ from the barren ones (a higher stage in development) . The fertile leaves are not confined to definite parts of the shoot, and do not limit its growth. The archesporium is most frequently unicellular. ”

“ The cells either live solitarily or are united into unbranched filaments. The mass of protoplasm formed by the fusion of the two conjugating cells becomes the zygote, which on germination produces one (or after division 2, 4 or 8) new vegetative individual. The chromatophores are either star-, plate-, or band-shaped, and regularly arranged round the long axis of the cell. ”

“ The honey is secreted in the perianth-tube, and the insects, endeavouring to obtain it through the narrow passages at the base of the stamens, settle upon the outer perianth-leaves, which are bent backwards and often very hairy along their central line. The insects then rub their backs on the anthers just above them, beneath the branches of the style; they readily deposit the pollen on the stigma of another flower as they enter it, but cannot do so in withdrawing, since the stigma is pushed back, and self-fertilisation is thus avoided. ”

“ A mycelium which has sprung from one spore, whose position is marked by the *: a, b, c are three sporangia in different stages of development; a is the youngest one, as yet only a short, thick, erect branch; b is commencing to form a sporangium which is larger in c, but not yet separated from its stalk.
[98]
The Mucoraceæ, in addition to the chlamydospores and oidia, have a more normal and ordinary method of reproduction; viz., by spores which are formed without any sexual act. Mucor has round sporangia ”

“ Uredinaceæ (Rusts) . All the Rust-Fungi are parasites, their mycelium living in the interior of the stems and leaves of their hosts, causing red, brown, or black spots—hence their name—and malformations, sometimes of considerable size.
The Rust-Fungi are gymnocarpic and destitute of a hymenium; for these reasons they are regarded as the simplest order of the Basidiomycetes. They are entirely parasitic, and their filamentous, branched mycelium ramifies in the intercellular spaces of its host, and often protrudes haustoria into the cells. The mycelium is perennial should it enter a woody tissue ”

“ The cells of the Bacteria are constructed like other plant-cells in so far as their diminutive size has allowed us to observe them. The cell-wall only exceptionally shows the reactions of cellulose (in Sarcina, Leuconostoc; also in a Vinegar-bacterium, Bacterium xylinum) ; a mucilaginous external layer is always present. The body of the cell mostly appears to be an uniform or finely granulated protoplasm. Very few species (e.g. Bacillus virens) contain chlorophyll; others are coloured red (purple sulphur Bacteria) ; the majority are colourless. ”