Common objects of the microscope

by J. G. Wood

In the centre of the Plate may be seen a wheel-like arrangement of the peculiar cells found on the petals of six different flowers, all easily obtainable, and mounted without difficulty.

Fig. [30] is the petal of a geranium (Pelargonium), a very common object on purchased slides. It is a most lovely subject for the microscope, whether it be examined with a low or a high power,—in the former instance exhibiting a most beautiful “stippling” of pink, white, and black, and in the latter showing the six-sided cells with their curious markings.

In the centre of each cell is seen a radiating arrangement of dark lines with a light spot in the middle, looking very like the mountains on a map. These lines were long thought to be hairs; but Mr. Tuffen West, in an interesting and elaborate paper on the subject, has shown their true nature. From his observations it seems that the beautiful velvety aspect of flower petals is owing to these arrangements of the surface cells, and that their rich brilliancy of colour is due to the same cause. The centre of each cell-wall is elevated as if pushed up by a pointed instrument from the under side of the wall, and in different flowers this elevation assumes different forms. Sometimes it is merely a slight wart on the surface, sometimes it becomes a dome, while in other instances it is so developed as to resemble a hair. Indeed, Mr. West has concluded that these elevations are nothing more than rudimentary hairs.

The dark radiating lines are shown by the same authority to be formed by wrinkling of the membrane forming the walls of the elevated centre, and not to be composed of “secondary deposit,” as has generally been supposed.

Fig. [31] represents the petal of the common periwinkle, differing from that of the geranium by the straight sides of the cell-walls, which do not present the toothed appearance so conspicuous in the former flower. A number of little tooth-like projections may be seen on the interior of the cells, their bases affixed to the walls and their points tending toward the centre, and these teeth are, according to Mr. West, formed of secondary deposit.

In Fig. [32] is shown the petal of the common garden balsam, where the cells are elegantly waved on their outlines, and have plain walls. The petal of the primrose is seen in Fig. [34], and that of the yellow snapdragon in Fig. [33]; in the latter instance the surface cells assume a most remarkable shape, running out into a variety of zigzag outlines that quite bewilders the eye when the object is first placed under the microscope. Fig. [35] is the petal of the common scarlet geranium.

In several instances these petals are too thick to be examined without some preparation, and glycerine will be found well adapted for that purpose. The young microscopist must, however, beware of forming his ideas from preparations of dried leaves, petals, or hairs, and should always procure them in their fresh state whenever he desires to make out their structure. Even a fading petal should not be used, and if the flowers are gathered for the occasion, their stalks should be placed in water, so as to give a series of leaves and petals as fresh as possible.

We now pass from the petal of the flower to the pollen, that coloured dust, generally yellow or white, which is found upon the stamens, and which is very plentiful in many flowers, such as the lily and the hollyhock.

This substance is found only upon the stamens or anthers of full-blown flowers (the anthers being the male organs), and is intended for the purpose of enabling the female portion of the flower to produce fertile seeds. In form the pollen grains are wonderfully diverse, affording an endless variety of beautiful shapes. In some cases the exterior is smooth and marked only with minute dots, but in many instances the outer wall of the pollen grain is covered with spikes, or decorated with stripes or belts. A few examples of the commonest forms of pollen will be found on Plate III.

Fig. [17] is the pollen of the snowdrop, which, as will be seen, is covered with dots and marked with a definite slit along its length. The dots are simply tubercles in the outer coat of the grain, and are presumed to be formed for the purpose of strengthening the membrane, otherwise too delicate, upon the same principle which gives to “corrugated” iron such strength in proportion to the amount of material. Fig. [18] is the pollen of the wall-flower, shown in two views, and having many of the same characteristics as that of the snowdrop. Fig. [19] is the pollen of the willow-herb, and is here given as an illustration of the manner in which the pollen aids in the germination of plants.