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CURIOSITIES OF VEGETABLE MORPHOLOGY.

BY HENRY J. SLACK, F.G.S., SEC. R.M.S.

[PLATE XCVI.]

ONE

NE of the most important sciences of quite modern growth is that of Morphology, the object of which is to trace the series of growth and development processes by which organs or structures are brought to their final form. This is done in both the vegetable and the animal kingdoms, and also in that border-land to which no definite name can be given, and in which organization appears in its simplest forms. The morphology of plants and animals is intimately connected with the comparative anatomy of the two groups, and the investigator traces step by step the formation of particular structures, notes the points at which they diverge to carry out the plan on which different types are built up, and the extent as well as the direction to which development is carried. By researches of this description-lower groups and higher onesare shown to be intimately connected, so that, as discovery follows discovery, the apparent gaps in the great scheme are gradually filled in, and little doubt left of the two great scientific doctrines-unity of design and gradual transformation of so-called species. The extinct forms preserved in a fossil state often help the morphologist as well as the comparative anatomist to a missing link, and no branch of enquiry is more intimately connected with speculative thought, or contributes more to a philosophical conception of Nature as a whole. As an illustration of the curious results arrived at, it may be mentioned that our great English morphologist, Mr. W. K. Parker, finds in the tadpole, in a rudimentary form, a structure belonging to the human ear.

There is of course very much in such a science as morphology that is beyond the reach of the student of popular science, but a good deal may be learned from plants, without much trouble, especially with the help of a microscope. The most agreeable and easy way of laying a foundation for further

enquiry is to notice the growth and final condition of certain parts or organs of different species of plants. Take for example the hairs found on leaves or flowers. They are all appendages of the cuticle, and vary from single cells to structures of many cells, arranged in a straight line, or in star patterns, more or less complicated, in single layers or in many. We also find them branched and knobbed. When filled with thin fluids they are soft; but they are capable of being strengthened and thickened into thorns, which are distinguished from spines as being outgrowths of the epidermis, not of the wood. They also exhibit in some cases deposits of silica. Many of these plant hairs are well known as microscopic objects; those on the leaves of Deutzia scabra, for example, being frequently used for exhibition with the polariscope. It is not, however, common to find in popular collections the flower-buds of this plant, or of D. gracilis, both of which are exquisite objects, especially the former. The young flower-bud should be mounted in a cell with glycerine jelly, and viewed as an opaque object with a binocular instrument of 14 or 1-inch objective. The stellate hairs (fig. 1) shine like silver, and their true form is much better seen than when they are compressed in the usual balsam mounting. Hairs of this description should be contrasted with simple tubular hairs, and also with those that branch, or terminate in knobs. The hair of the cabbage-leaf is a good illustration of the simplest form. Those on the calyx of Salvia have bulbous heads, and those on the stems of London Pride exhibit minute terminal bulbs, filled with a fine ruby fluid. Many of the Crucifera have branched hairs. On the stalk of the Deutzia flower-buds will be seen long hairs like thorns, but not so hard, and surrounded at their basis with lesser hairs in star patterns. The Deutzia hairs should not be dismissed without taking some leaves of the plant and calcining them over a spirit-lamp. Those who possess chemical apparatus will find a platina or small porcelain crucible convenient for this purpose; but it may be effected on a plate of brass or sheet iron. The black carbonaceous mass left when the process is finished is excessively brittle, but a few of the flattest pieces may be placed in a shallow cell, some with the upper and some with the lower side at top, covered with thin glass, and viewed as opaque objects. The hairs look like a lot of steel-gray star-fishes, and their minute tubercles, which are well preserved, add to the resemblance.

Amongst the hairs found on sepals, those of the Gum Cistus are particularly beautiful and curious (fig. 2). The cuticles of these sepals should be cut off in thin slices with a fine pair of sharp scissors, and mounted in glycerine jelly, without compression. They are then transparent enough to show in the

usual way with the polariscope, lit up with rich colours; or they may be viewed with ordinary light, either as opaque or transparent objects. Each hair is simple, something like that of the cabbage, but a considerable number grow out from a common base, forming radiating tufts.

Having considered hairs in simple and compound forms, as soft structures and as hardened into thorns, the transitions from hairs to scales should be observed; and many ferns will supply good illustrations. The hairs on the stems of the large parti-coloured-leaved Begonias are thickly furnished with hairs, composed of a multitude of cells, looking somewhat like scales to the naked eye, but under the microscope they exhibit a complicated cell-structure, and show how easy it is to pass from simple hairs to higher forms.

Many hairs are glandular; that is, they act like glands, and secrete some peculiar material. The best known is that of the stinging-nettle, providing the acrid poison that escapes as soon as a slight touch breaks off the brittle point. Hairs that secrete and store up remarkable colouring matters will be readily found by examining plants on the roadside or in the garden. A common St. John's Wort (Hypericum pulchrum) has its leaves furnished with a fringe of club-shaped glands, similar in structure to many stumpy hairs, and filled with dark pigment (Fig. 4.) Interesting hairs with glandular tips will be found on the sepals of the American Currant (Ribes sanguineosum), common as an ornamental shrub.

The surface glands of leaves are essentially the same in construction as hairs, being expansions of the cuticle. They differ from the deeper glands (internal glands) below the cuticle, which can be well seen in a vertical section of orange-peel. The ornamental Coleus plants, common in every conservatory, afford interesting specimens of surface or cuticular glands. The under surface of the leaves should be examined as opaque objects with powers of from 60 to 100 or more, and numerous little balls, slightly indented with a cross, will be seen to shine like topaz gems. They may be found well developed in very young leaves; and such leaves, if also adorned with numerous hairs, filled with purple and white fluids, make splendid objects when well lit up. The little glands contain a fluid that seems to pass into a resinous state, changing to a redder tint when simply dried. A leaf flattened and dried in a book, then placed on a slide covered with thin glass, with paper pasted round the edges, or the edges cemented with varnish, keeps its colour sufficiently well to be worth preserving. In a specimen before the writer at this moment, put up a year ago, the glandular balls have retained their form and size very closely, changing to a darker tint, and the hairs with which the leaf is