Common objects of the microscope

by J. G. Wood

Fig. [9] is a beaded hair from the Marvel of Peru, which is composed of a number of separate cells placed end to end, and connected by slender threads in a manner that strongly reminds the observer of a chain of beads strung loosely together, so as to show the thread by which they are connected with each other. Another good example is seen at Fig. [11], in a hair taken from the leaf of the sowthistle. In this case the beads are strung closely together, and when placed under a rather high power of the microscope have a beautifully white and pearly aspect. The leaf must be dry and quite fresh, and the hairs seen against the green of the leaf. Fig. [39] represents another beaded hair taken from the Virginian Spiderwort, or Tradescantia. This hair is found upon the stamens, and is remarkable for the beautifully beaded outline, the fine colouring, and the spiral markings with which each cell is adorned.

A still further modification of these many-celled hairs is found in several plants, where the hairs are formed by a row of ordinarily shaped cells, with the exception of the topmost cell, which is suddenly elongated into a whip-like form. Fig. [22] represents a hair of this kind, taken from the common groundsel; and Fig. [36] is a still more curious instance, found upon the leaf of the thistle. The reader may have noticed the peculiar white “fluffy” appearance of the thistle leaf when it is wet after a shower of rain. This appearance is produced by the long lash-like ends of the hairs, which are bent down by the weight of the moisture, and lie almost at right angles with the thicker portions of the hair.

An interesting form of hair is seen in the “sting” of the common nettle. This may readily be examined by holding a leaf edgewise in the stage forceps, and laying it under the field of the microscope. In order to get the proper focus throughout the hair, the finger should be kept upon the screw movement, and the hair brought gradually into focus from its top to its base. The general structure of this hair is not unlike that which characterises the fang of a venomous serpent. The acrid fluid which causes the pain is situated in the enlarged base of the hair, and is forced through the long straight tubular extremity by means of the pressure exerted when the sting enters the skin. At the very extremity of the perfect sting is a slight bulb-like swelling, which serves to confine the acrid juice, and which is broken off on the least pressure. The sting is seen in Fig. [43].

The extremities of many hairs present very curious forms, some being long and slender, as in the examples already mentioned, while others are tipped with knobs, bulbs, clubs, or rosettes in endless variety.

Fig. [12] is a hair of the tobacco leaf, exhibiting the two-celled gland at the tip, containing the peculiar principle of the plant, known by the name of “nicotine.” The reader will see how easy it is to detect adulteration of tobacco by means of the microscope. The leaves most generally used for this purpose are the dock and the cabbage, so that if a very little portion of leaf be examined the character of the hairs will at once inform the observer whether he is looking at the real article or its substitute.

Fig. [15] is a hair from the flower of the common yellow snapdragon, which is remarkable for the peculiar shape of the enlarged extremity, and for the spiral markings with which it is decorated. Fig. [16] is a curious little knobbed hair found upon the moneywort, and Fig. [17] is an example of a double-knobbed hair taken from the Geum. Fig. [34] affords a very curious instance of a glandular hair, the stem being built up of cells disposed in a very peculiar fashion, and the extremity being developed into a beautiful rosette-shaped head. This hair came from the Garden Verbena.

Curiously branched hairs are not at all uncommon, and some very good and easily obtained examples are given on Plate II.

Fig. [28] is one of the multitude of branched hairs that surround the well-known fruit of the plane-tree, the branches being formed by some of the cells pointing outward. These hairs do not assume precisely the same shape; for Fig. [29] exhibits another hair from the same locality, on which the spikes are differently arranged, and Fig. [30] is a sketch of another such hair, where the branches have become so numerous and so well developed that they are quite as conspicuous as the parent stem.

One of the most curious and interesting forms of hair is that which is found upon the lavender leaf, and which gives it the peculiar bloom-like appearance on the surface.

This hair is represented in Figs. 40 and 41. On Fig. [40] the hair is shown as it appears when looking directly upon the leaf, and in Fig. [41] a section of the leaf is given, showing the mode in which the hairs grow into an upright stem, and then throw out horizontal branches in every direction. Between the two upright hairs, and sheltered under their branches, may be seen a glandular appendage not unlike that which is shown in Fig. [16]. This is the reservoir containing the perfume, and it is evidently placed under the spreading branches for the benefit of their shelter. On looking upon the leaf by reflected light the hairs are beautifully shown, extending their arms on all sides; and the globular perfume cells may be seen scattered plentifully about, gleaming like pearls through the hair-branches under which they repose. They will be found more numerous on the under side of the leaf.