means of obtaining these low forms of vegetation is to collect a quantity of Duckweed, "the green mantle of the standing pool," from the surface of a stagnant pond, together with some of the water. If a single plant of Duckweed be put on a glass slip and covered with the thin glass used for the purpose, then placed under the microscope, a number of distinct forms will be seen some vegetable, some animal. With the latter we have nothing to do in the present volume; we shall simply ignore them.

Most of the minute plants found in ponds belong to the same tribe as the Seaweeds (the Alga), but we shall also have something to say of the tiny representatives of the Mushroom family (the Fungi), low forms of which abound on all decaying sub

stances.

One of the simplest of the Algæ—and one of the most plentiful-is the Protococcus. Our readers will probably be struck with the fact that these very small plants have very large names. We hope they will not be frightened, for, after all, it is a small matter; and when they are learnt, they give us some fact about the owner, such as it would take many words in English to make clear. In this instance it means literally first berry or plant, that is, the simplest form of plant. It is found in abundance in ponds, ditches, rain-water butts, and in fact wherever water accumulates in little pools. It consists of a single cell or sac containing a jelly-like substance called. protoplasm. It is this protoplasm which constitutes the living part of the plant; the covering (cell) cannot grow, it requires to be added to by the proto

plasm secreting fresh deposits of it. Some of the specimens, you will notice, are coloured green, some red, and others parti-coloured. This is owing to certain portions or granules of the protoplasm being covered with a peculiar pigment called chlorophyll (leaf-colour), which is either green or red. The cellwall itself, though seemingly coloured, is colourless. If we examine a number of these with our microscopes we shall probably be able to observe the manner in which the plant is increased, for it does not produce seeds like flowering plants. The alternative plan adopted by the gardener to increase his stock of plants is to take cuttings from them, and we find that a somewhat similar process goes on in this Protococcus, for it divides itself into two parts, and then again into four. This cut will show you how it is done. A partition forms across the protoplasm, and thus two cells are formed inside the old cell-wall; these two cells. divide in the same manner, and the old cell-wall bursts, setting free four perfect protococci. Sometimes, though rarely,

α

d

P--

b

FIG. 1.

a little protuberance or swelling is formed at one part of the plant, and, gradually increasing in size, assumes a round form, and ultimately becomes separated from the parent cell. At times a remarkable change takes place in this plant. The protoplasm penetrates the cell-wall at two points, and protrudes in the form of two long, slender filaments (cilia), which, being kept constantly moving, propel the

cell rapidly along. Like many other of these minute forms of life, Protococci are not easily destroyed. Shallow pools containing them may be thoroughly dried up by a very hot summer, yet as soon as rain falls the Protococci may be found there in profusion. When in a dry state they are often carried long distances by the wind, and, catching on any damp surface, quickly increase in numbers. Consequently, one has but to look in damp places to find a profusion of them. If we care to experiment a little with this one-celled plant, we may find out much that will be useful to us in the study of Physiological Botany. If, for instance, we place some Protococci in rainwater, and watch them from day to day, we shall observe that they thrive well, and multiply rapidly. This proves that the Protococcus can build up its cell-wall and protoplasm out of the substances contained in the rain-water. Now the only substances found in fresh rain-water are carbonic anhydride, ammonium nitrate, and a few mineral salts which were suspended in the air as dust; and a chemist would tell us that the protoplasm consists of a substance called protein, fat, and mineral salts, whilst the cell-wall is composed of cellulose and a few of the mineral salts. This chemist may be a very clever man, but if you ask him to make some protein, fat, or cellulose out of the carbonic anhydride, ammonium nitrate, &c., he will honestly acknowledge his inability to do so, because protein, fat, and cellulose are organic compounds, and only to be found in animal or vegetable substances. From this we are forced to the conclusion that some remarkable

changes must go on in this tiny cell to enable it to build up its protoplasm and cell-wall out of such seemingly unpromising material; and perhaps in the course of our microscopical researches we may come across some plants which will throw a little more light upon this subject; but for the present we must bid adieu to Protococcus, and see what else we have under our microscope.

A long narrow rod, with transparent walls ornamented with spiral bands of green. It is one of the Yoke-threads or Con

ferva, those minute

hair-like plants you have so often seen

FIG. 2.

in ponds. You observe it is made up of a number of joints; these are cells, each like a protococcus with its sides flattened. The spiral ornament is really the protoplasm so arranged round the interior of the cell-wall. Each cell is capable of sustaining life, and giving rise to a new plant. They increase in length by the cells dividing across their width; they increase in numbers by the protoplasm becoming broken up into many little oval bodies, each provided with two cilia or hair-like appendages, by the constant lashing of which they propel themselves through the water. When the protoplasm becomes thus broken up, the cell-wall opens and sets them free, each one ultimately becoming a separate plant. It is called the Zygnema, a term which signifies yoke-thread.

By gently moving our glass slide we become aware of the presence of another of the same tribe of plants

-Conferva-one of the Oscillatoriæ. It is very similar in appearance to Zygnæma, but is much narrower, and the cells are very

FIG. 3.

short. Now look at them under the microscope;

they are gently moving over each other in all directions. It is from

this peculiarity-this oscillating motion-they derive Mr. Berkeley says of this tribe of

their name.

plants :"Oscillatoriæ grow in various situations-in salt and fresh water, on damp ground, amongst grass on close-shaved lawns, like lichens on the trunks of trees, floating on the surface of lakes and seas, or suspended like a cloud, giving rise to variously coloured waters. One or two fine purple species form thick woolly fleeces in the hotter parts of India, while many inhabit hot springs."

You think it strange that these low forms of plant life should have the power of motion, but that is only because you have been in the habit of observing large trees and bushes which are fixed to the ground by strong branched roots. Yet even these have certain powers of movement—at any rate, during portions of their lives. Have you not observed how plants bend towards the light, and how some that in the morning inclined to the east, in the evening lean to the west ? Then look at climbing plants, how they move round a stick or string. Mr. Darwin, the great naturalist, has written a book devoted entirely to the "Movements and Habits of Climbing Plants," and probably