Common objects of the microscope

by J. G. Wood

This singular plant has been greatly bandied about between the vegetable and animal kingdoms, but seems now to be satisfactorily settled among the vegetables. In the summer it may be found in pools of water, sufficiently large to be visible to the naked eye, like a little green speck proceeding slowly through the water. When a moderate power is used, it appears as shown in the figure, and always contains within its body a number of smaller individuals, which after a while burst through the envelope of the parent and start upon an independent existence. On a closer examination, a further generation may be discovered even within the bodies of the children. The whole surface is profusely covered with little green bodies, each being furnished with a pair of movable cilia, by means of which the whole organism is moved through the water. These bodies are analogous to the zoospores already mentioned, and are connected with each other by a network of filaments. Reproduction also takes place by conjugation as in other algæ. A more magnified representation of one of the green bodies is shown immediately above the larger figure. The volvox is apt to die soon when confined in a bottle.

Fig. [25] is the common yeast-plant, consisting simply of a chain of cells, which increase by budding, and only form spores when they have exhausted the nutriment in the fluid in which they live. Fig. [26] is a curious object, whose scientific name is Sárcina ventrículi. It is found in the human stomach. Similar forms are often to be found in the air; for instance, a piece of cocoa-nut will exhibit this, and many other kinds of Bacteria and moulds, after a few days’ exposure to the air, preferably in a dark cupboard.

We now come upon a few of the blights and mildews. A very interesting series of forms is first to be alluded to. Upon the bramble-leaf may often be found spots, at first red, then orange, then reddish black. These are known as Œcidium berberidis. Fig. [32] shows the “red-rust” of wheat, the Urédo; and Fig. [33] is the mildew of corn, known as Puccinia. The interest lies in the fact that these three forms are successive stages in the life-history of the same plant. Another species of Urédo, together with a Phragmídium, once thought to be another kind of fungus, is seen on a rose-leaf on Plate V. Fig. [1]. On Fig. [10], however, of the same Plate, the Phragmídium may be seen proceeding from Urédo, thus proving them to be but two states of the same plant. There is room for any amount of observation and work in connection with the life-histories of many of these fungi.

Another species of Puccinia, found on the thistle, is shown on Plate V. Fig. [7]. Fig. [34] is the mould found upon decaying grapes, and called therefrom, or from the clustered spores, Botrýtis. Some of the detached spores are seen by its side. Fig. [35] is another species of the same genus, termed Botrýtis parasítica, and is the cause of the well-known “potato-disease.”

The mosses and ferns afford an endless variety of interesting objects to the microscopist; but as their numbers are so vast, and the details of their structure so elaborate, they can only be casually noticed in the present work. Fig. [38] represents a spore-case of the Polypodium, one of the ferns, as it appears while in the act of bursting and scattering the contents around. One of the spores is seen more magnified below. The spore-cases of many ferns may be seen bursting under the microscope, and have a very curious appearance, writhing and twisting like worms, and then suddenly filling the field with a cloud of spores. Fig. [9], Plate V., is a piece of the brown, chaff-like, scaly structure found at the base of the stalk of male fern cells, showing the manner in which a flat membrane is formed. Fig. [39] is a capsule of the Hypnum, one of the mosses, showing the beautiful double fringe with which its edge is crowned. Fig. [2], Plate V., is the capsule of another moss, Polytríchum, to show the toothed rim; on the right hand is one of the teeth much more magnified.

Fig. [3], Plate V., is the capsule of the Jungermannia, one of the liverworts, showing the “elaters” bursting out on every side, and scattering the spores. Fig. [4] is a single elater much magnified, showing it to be a spirally coiled filament, that, by sudden expansion, shoots out the spores just as a child’s toy-gun discharges the arrow. Fig. [5] is a part of the leaf of the Sphagnum moss, common in fresh water, showing the curious spiral arrangement of secondary fibre which is found in the cells, as well as the circular pores which are found in each cell at a certain stage of growth. Just below, and to the left hand, is a single cell greatly magnified, in order to show these peculiarities more strongly. Fig. [8] is part of a leaf of Jungermannia, showing the dotted cells.

Fig. [6], Plate V., is a part of a rootlet of moss, showing how it is formed of cells elongated and joined end to end.

On the common mare’s-tail, or Equisétum, may be seen a very remarkable arrangement for scattering the spores. On the last joint of the stem is a process called a fruit-spike, being a pointed head around which are set a number of little bodies just like garden-tables, with their tops outward. One of these bodies is seen in Fig. [40]. From the top of the table depend a number of tiny pouches, which are called sporangia; these lie closely against each other, and contain the spores. At the proper moment these pouches burst from the inside, and fling out the spores, which then look like round balls with irregular surfaces, as shown in Fig. [40], c. This irregularity is caused by four elastic filaments, knobbed at the end, which are originally coiled tightly round the body of the spore, but by rapidly untwisting themselves cause the spore to leap about, and so aid in the distribution. A spore with uncoiled filaments is seen at Fig. [40], b. By breathing on them they may be made to repeat this process at will.

Fig. [36] is a common little sea-weed, called Ectocarpus siliculósus, that is found parasitically adhering to large plants, and is figured in order to show the manner in which the extremities of the branches are developed into sporangia. Fig. [37] is a piece of the common green laver, Ulva latíssima, showing the green masses that are ultimately converted into zoospores, and by their extraordinary fertility cause the plant to grow with such rapid luxuriance wherever the conditions are favourable. Every possessor of a marine aquarium knows how rapidly the glass sides become covered with growing masses of this plant. The smaller figure above is a section of the same plant, showing that it is composed of a double plate of cellular tissue.

Fig. [41] is a piece of purple laver or “sloke,” Porphýra laciniáta, to show the manner in which the cells are arranged in groups of four, technically named “tetraspores.” This plant has only one layer of cells.