Common Objects of the Microscope. John George Wood

them in many familiar garden vegetables, such as the common radish, which is very prolific in these interesting portions of vegetable nature.

      There is another remarkable form in which this secondary deposit is sometimes arranged that is well worthy of our notice. An example of this structure is given in Fig. 18, taken from the stalk of the common fern or brake. It is also found in very great perfection in the vine. On inspecting the illustration, the reader will observe that the deposit is arranged in successive bars or steps, like those of a winding staircase. In allusion to the ladder-like appearance of this formation, it is called “scalariform” (Latin, scala, a ladder).

      In the wood of the yew, to which allusion has already been made, there is a very peculiar structure, a series of pits found only in those trees that bear cones, and therefore termed the coniferous pitted structure. Fig. 16 is a section of a common cedar pencil, the wood, however, not being that of the true cedar, but of a species of fragrant Juniper. This specimen shows the peculiar formation which has just been mentioned.

      Any piece of deal or pine will exhibit the same peculiarities in a very marked manner, as is seen in Fig. 24. A specimen may be readily obtained by making a very thin shaving with a sharp plane. In this example the deposit has taken a partially spiral form, and the numerous circular pits with which it is marked are only in single rows. In several other specimens of coniferous woods, such as the Araucaria, or Norfolk Island pine, there are two or three rows of pits.

      A peculiarly elegant example of this spiral deposit may be seen in the wood of the common yew (Fig. 17). If an exceedingly thin section of this wood be made, the very remarkable appearance will be shown which is exhibited in the illustration. The deposit has not only assumed the perfectly spiral form, but there are two complete spirals, arranged at some little distance from each other, and producing a very pretty effect when seen through a good lens.

      The pointed, elongated shape of the wood-cells is very well shown in the common elder-tree (see Fig. 15). In this instance the cells are without markings, but in general they are dotted like Fig. 21, an example cut from the woody part of the chrysanthemum stalk. This affords a very good instance of the wood-cell, as its length is considerable, and both ends are perfect in shape. On the right hand of the figure is a drawing of the wood-cell found in the lime-tree (Fig. 22), remarkable for the extremely delicate spiral markings with which it is adorned. In these wood-cells the secondary deposit is so plentiful that the original membranous character of the cell-walls is entirely lost, and they become elongated and nearly solid cases, having but a very small cavity in their centre. It is to this deposit that the hardness of wood is owing, and the reader will easily see the reason why the old wood is so much harder than the young and new shoots. In order to permit the passage of the fluids which maintain the life of the part, it is needful that the cell-wall be left thin and permeable in certain places, and this object is attained either by the “pits” described on page 43, or by the intervals between the spiral deposit.