Zoospore

“ In coenocytic forms the zoospores would seem to arise simultaneously, probably because many nuclei are already present. The escape of zoospores is effected by the degeneration of the sporangial wall (Chaetophora) , or by a pore (Cladophora) , a slit (Pediastrum) , or a circular fracture (Oedogonium) . Zoospores are of two kinds: (1) Those which come to rest and germinate to form a new plant; these are asexual and are zoospores proper. (2) Those which are unable to germinate of themselves, but fuse with another cell, the product giving rise to a new individual ”

“ Pinoy's results indicate, though not so conclusively, that bacteria are likewise the essential food of the Euplasmodida in the early phases of their life-history. The zoospores do, however, ingest other solid bodies, e.g. carmine granules (Saville Kent, 15) .
The zoospores multiply by binary fission the flagellum being withdrawn and the nucleus undergoing mitotic division, with the formation of a well-marked achromatic spindle (fig. 3) .
It is probable that fission occurs more than once in the zoospore stage; but there is not satisfactory evidence to show how often it may be repeated. ”

“ From very similar spore cases a number of zoospores are liberated and for a time they swim about freely. If now we watch carefully we shall notice that one of the active little bodies comes to rest and that the others lose no time in swarming round it. ”

“ It is believed that the brood-cells from the same parent will not unite together. The contents of each spore have again undergone brood-division to form eight sickle-shaped zoospores, or "sporozoites" (n-q) , and thus the developmental cycle is completed. Probably the spores, swallowed by birds, pass out in their excrement, and when eaten by an earthworm open in its gut; the freed sickle-germs can now migrate through the tissues to the seminal funnels, in the cells of which they grow, ultimately becoming free in the seminal vesicles. ”

“ Ulothrix. a, Vegetative Filament. b, Development of Asexual Zoospores. c, Zoospore, d, Sporelings. e, Cell containing Gametes. f, Gametes, g, Conjugation of Gametes, h, Sexually formed Spore. many months, but at times the conditions are such that another form of swarm-spore appears. These elements are much smaller than the usual zoospores, are developed more numerously in the mother cell and have 2 cilia as is shown in Figure 2, e, f. They are gametes and as a rule fuse readily with one another in pairs. ”

“ The generation of the zoospores commences within from an hour and a half to three hours after the sowing of the conidia on water. From the oogonia, or resting spores, similar zoospores, but in greater number, are generated in the same manner, and their conduct after becoming free is identical. Their movements in the water usually last from two to three hours, then they abate, the cilia disappear, and the spore becomes immovable, takes a globose form, and covers itself with a membrane of cellulose. ”

“ In many of them we find instances of that strange process of reproduction by means of zoospores, or moving spores, which so often occurs among their green-spored relations. The zoospores may be well seen in the plants which belong to the genus Ectocarpus, one or two species of which are very common in the summer, spreading in a matted mass over rocks and larger seaweeds, and looking when left by the tide like a layer of withered and rotting leaves. The moving spores are formed in the last cell of each of the fine threads of which the plant is composed. ”

“ Nets with strong inclinations to form zoospores can be made to produce gametes by cultivating in a sugar solution in subdued light or darkness. Plants that have no special inclination to form either zoospores or gametes may be decided one way or the other by the illumination, bright light producing zoospores and darkness gametes. It is also fair to say that sometimes the tendency to form zoospores is so strong that a plant will not yield for several generations to the conditions that generally bring about the immediate production of gametes. ”

“ The erect branched threads bear at the tip of their branchlets spores, or conidia, which conduct themselves in a like manner to the organs so named in Cystopus, and oogonia or resting spores developed on the mycelium within the tissues of the foster plant also give origin to similar zoospores. ”

“ Those zoospores which are furnished with cilia at one extremity only, direct that extremity, which is destitute of chlorophyll or green coloring-matter, toward the light. Closely resembling these zoospores are the "spermatozoa" of the higher orders of cryptogamic plants, ferns, equisetums, and mosses. These bodies (Fig. 2) are produced in the antheridia or male organs, again by a modification of the protoplasmic cell-contents ”

“ The eminent botanist, De Bary, who was not thinking of our problem, tells us, in describing the movements of these "Zoospores," that, as they swim about, "foreign bodies are carefully avoided, and the whole movement has a deceptive likeness to the voluntary changes of place which are observed in microscopic animals." ”

“ If we are either fortunate or exceptionally patient we may chance to be examining one of these swellings under the microscope at the moment when it bursts and sets free its contents. Should we have this good fortune we must hasten to magnify more highly the zoospores which have escaped from the pear shaped spore case. Here we may add the caution that we shall only witness the bursting of the spore case if we examine our specimen in sea water; we should require more than the patience of Job to watch for its bursting in the dry state, for it will never come to pass. ”

“ When the free ends of the hyphae emerge again into the air they swell up into spherical bodies which may either fall off and behave as conidia, each putting out a germ-tube and infecting the host; or the germ-tube itself swells up into a zoosporangium which develops a number of zoospores. ”

“ But if we carry our observations a little further we shall find ample reason for rejecting as inadmissible any theory involving a belief in the animal nature of the zoospores. If these moving spores are really, as we have supposed, the produce of the ulva, we may expect that they will at some period of their existence grow into the likeness of their parent. ”

“ Take a small glass cell containing a few drops of sea-water and some of the zoospores, and, in order to prevent the water from evaporating, place the cell upon a layer of moist sand and cover it with a bell-glass or a tumbler, and you will be able to preserve the zoospores alive for any length of time, and to trace from time to time any changes which take place in them. ”

“ Very soon, however, they begin to move, and then vibratile cilia show themselves (d) , and by means of these appendages the entire globule moves in an oscillating manner as one by one the zoospores disengage themselves, each becoming isolated and swimming freely in the surrounding fluid. The movement is precisely that of the zoospores of Algæ. ”

“ But in the act of propagation, on the contrary, and when about to pass into the still condition, the motile Protococcus cell seems to shun light, and falls to the bottom of the vessel. Too strong sunlight, as when concentrated by a lens, quickly kills the young zoospores. A temperature of undue elevation is injurious to the development of their vital activity and the formation of the zoospores. Frost destroys motile, but not still zoospores.55
Stephanosphæra pluvialis is a conspicuous variety of the fresh-water algals, described by Cohn. ”

“ Usually, however, only one of the fusing cells is a zoogamete, the other gamete being a much larger resting cell. In such a case the zoogamete is male, is called an antherozoid or spermatozoid, and arises in an antheridium; the larger gamete is an oosphere and arises in an oogonium. The fusion is now known as fertilization, and the product is an oospore. Reproduction by conjugation is also known as isogamy, by fertilization as oogamy. When zoospores come to rest, a new cell is formed and germination ensues at once. ”

“ Sexual reproduction takes place by zygospores, which function as resting-spores, and arise in consequence of conjugation (Fig. 81) ; in the majority of species these are rarely found, and only under special conditions. The most common method of reproduction is by endospores, by acrogenous conidia, by chlamydospores, or by oidia. Swarmspores are wanting. Parasites and saprophytes (order 6 and 7) . The zygospores are generally produced when the formation of sporangia has ceased; e.g. by the suppression of the sporangial-hyphæ (Mucor mucedo) , or by the diminution of oxygen ”

“ Morphologically considered, spores are marked by peculiarities of form, size, colour, place of origin, definiteness in number, mode of preparation, and so forth, such that they can be distinguished more or less sharply from the hyphae which produce them. The only physiological peculiarity exhibited in common by all spores is that they germinate and initiate the production of a new fungus-plant. Whether a spore results from the sexual union of two similar gametes (zygospore) or from the fertilization of an egg-cell by the protoplasm of a male organ (oospore) ”

“ In addition, the great majority have also another method of reproduction, for increasing the number of the parasites in any individual host; this is distinguished as multiplicative or endogenous reproduction, from the propagative or exogenous method (by means of the resistant spores) , which serves for the infection of fresh hosts and secures the dissemination and survival of the species. Further, most if not all forms of Sporozoa undergo sexual conjugation at some period or other of the life-cycle. ”

“ The principal food-supply of the larva consists of the spores of fresh-water algae, diatoms, particles of Spirogyra, and any other organisms which do not penetrate the surface-film. Occasionally the larvae devour the decaying leaves of duck-weed (Lemna) , and sometimes they attack their dead fellows.
Grassi found the intestine of the larva [Pg 85] to contain protozoa, unicellular algae, and other organic detritus. In course of time some object too big for the larva to swallow is brought to its mouth by the currents, but after a very short struggle this is rejected. ”

“ As the name implies, the spores of the Haplosporidia are simple, without polar capsules, and are uninucleate. In some genera, e.g., Haplosporidium, Urosporidium (fig. 111) there is a spore-coat or sporocyst which may be elongate or spiny. The developmental cycle of a Haplosporidian, such as Haplosporidium or Bertramia, begins with a small, uninucleate cell, often rounded, possessing a cell membrane that may be prolonged into processes. Growth takes place, coupled with an increase in the number of nuclei, so that a multinucleate trophozoite is produced. ”

“ Internal parasites and "saprophytes," that is, beings which live on dead and decayed organic matter, on the other hand, live surrounded by a supply of dissolved food; and rarely do we find larger cells, richer in reserves, than in the parasitic Sporozoa, which owe their name to the importance of brood-formation in their life-history. In Radiolaria (p. 75 f.) a central capsule separates off an inner layer of protoplasm; the outer layer is the one in which digestion is performed, while the inner layer stores up reserves; and here brood-formation appears to be the rule. ”

“ On the other hand, attachment may be transient (conjugation) when, after the exchange of portions of the nucleus, the couple separate, to multiply independently of each other. Sometimes there is an ALTERNATION OF GENERATIONS, as there may be several methods of propagation combined in the same species, either direct multiplication, conjugation, or copulation being practised; the different generations may thus, in certain cases, be unlike morphologically.
Protozoa inhabit salt water as well as fresh water; they are also found on land in very damp places, and invade animals as parasites. ”

“ A number of diseases in man and other animals are due to the presence of these Sporozoans, for they are all parasitic. Few if any animals are exempt from their attacks. They even attack other minute Protozoa. One hundred and fifty-seven species have been recorded as attacking insects, one hundred species attack birds, fifty-two reptiles, eighty crustaceans, twenty-two fish, and so through the list. Ten have been recorded as attacking man. In some instances the parasite is always present in the host and some hosts may harbor several different species of Sporozoa. ”

“ ECTOSPORA, a homogeneous and natural division of Protozoan parasites included under the Sporozoa; they comprise the three orders, Gregarines, Coccidia and Haemosporidia. The defining character of the Ectospora is that the spore-mother-cells (sporoblasts) are formed at the periphery of the parent-individual (sporont) ; we may, however, go further, and say that the formation of all the different reproductive elements is uniformly peripheral or exogenous. ”

“ In one section, the spores (which occupy nearly the same position, and perform similar functions, to the seeds of higher plants) are naked; that is, they are produced on spicules, and are not enclosed in cysts or capsules. This section is called Sporifera, or spore-bearing, because, by general consent, the term spore is limited in fungi to such germ-cells as are not produced in cysts. The second section is termed Sporidiifera, or sporidia-bearing, because in like manner the term sporidia is limited to such germ-cells as [Pg 65] are produced in cells or cysts. ”

“ These spores have by themselves no more power of growing into a new plant than the antherozoids; like them, left to themselves, they soon decay. It is only by the union of the two that a new plant can be produced. In the species which we have been describing, this union takes place within the frond, and it is therefore very difficult to get a peep at the process. But in the equally common Bladder-wrack, the antherozoids and spores are always found on distinct plants, and the fructification of the spores takes place after they have been discharged from the frond. ”