The star-shaped hairs on a potato leaf make beautiful objects for the microscope. Leaves of many plants are clothed with curious hairs.
4. Spirogyra
A green thread-like water weed. Two threads are shown fusing together; from each part of these fused threads a new plant will arise.
Small wonder that scientists were in doubt concerning the true nature of Euglena, its non-walled cell and peculiar mode of feeding are indeed puzzling. There are many similar cases amongst these lowly organisms, in fact there are some creatures which may best be described as partly plant and partly animal. Those of our readers who are interested in such problems may read an excellent account given much more fully than we could give it here, in Professor F. W. Keeble’s Plant Animals, one of the excellent Cambridge Manuals of Science. The fact is that the demarcation between plants and animals, low in the scale of development, is not nearly so pronounced as it is amongst the higher forms of life. Amongst the plants of our pond we shall find that, like the land plants, most of them are green, and many of them are thread-like, so that the task of distinguishing one from another may appear difficult. Examined with the naked eye, many of them appear remarkably similar to one another; under the microscope the differences are obvious.
One of the most remarkable of the commoner pond plants is known as Oscillatoria; it does not boast of a popular name but its scientific name is not very difficult to remember after we have witnessed its oscillations. Oscillatoria is a plant with particularly animal-like movements. It is merely a thread, usually green-blue in colour, but sometimes red or violet. The threads are never branched and, except when in motion, are straight. Under a moderately high magnification we can see that this thread-like plant is not composed of a single cell but that it consists of a number of cells, placed end to end. Sometimes a few of these cells will break away and start life on their own account.
Whatever interest the structure of Oscillatoria may have for us, we cannot help being struck with its movements, and we must make a point of observing them. The movement is peculiar and not easy to describe nor, so far as we know, has it ever been explained. A thread will be seen to glide backwards and forwards, becoming somewhat curved and, at the same time, revolving on its axis. Eel-like is perhaps a good description of the movement. It is possible to distinguish this plant from other pond dwellers by its slimy “feel” which arises from the fact that each thread is enclosed in a jelly-like sheath.
The silk weeds, Cladophora Glomerata are somewhat similar in appearance to the plant we have just described, but they are denizens of running streams rather than of ponds. They are the green thread-like plants we so often see attached by one end to rocks and stones beneath running water. Each plant consists of a long, cylindrical structure composed of several cells. We mention the silk weeds here, because they are best of all plants for showing cell growth. This growth takes place at or near the unattached end of the plant and is easily observed. The end cell may be watched for the process. Its green contents will be observed to contract in the middle so that it assumes an hour-glass shape. Then, where the contraction has taken place, we can watch the formation of a wall right across the cell, so that when the process is completed we have two cells where formerly there was one. More rarely, the contents of a cell will be observed to bulge out a side wall, then a new wall is formed to divide it off from the main cell and thus the beginning of a branch is formed. The silk weeds exhibit no movements, except such as are imparted to them by the running water.
A very beautiful little pond plant is known to science as Draparnalda Glomerata. We shall probably forget its name, but we can never forget the plant itself when once we have been fortunate enough to see it. A single row of large, transparent cells, containing very little green colouring matter, forms the main part of the plant. At regular intervals from these transparent cells, there arise rings of deep green branches, each one tipped with an extraordinarily long, colourless hair. Draparnalda is indeed a plant worth looking for.
Two common little green plants grow so near to the edges of ponds that they may well be included amongst our pond plants. The simpler of the two, known as Vaucheria Sessilis thrives on almost any damp soil and may even form a covering on soil in pots. In structure, Vaucheria is very simple for it consists of a single, frequently branched, tubular cell. The little attaching organ, by means of which the plant fixes itself to some firm support, is colourless, so too is the tip of the cell where growth takes place.
We must examine this little plant when we come across it and we must not fail to notice that it is composed of but one cell. The only time at which we can find any cross walls, is when Vaucheria is about to increase. Then the tip of the cell swells, like a little club, and a cross wall separates it from the rest of the plant. The contents of this cell rounds itself off, becomes fringed with innumerable little lashing whips and escapes from a pore at the tip of the cell in which it was formed. This little organism swims about for a time in the water, for Vaucheria only increases in this manner when it is under water, at length it comes to rest and forms a new plant.