The grasses seem to have been the means of revealing the earliest dawn of plant life, for the Hon. Sidney Osborne discovered that the colourless protoplasm, or organizable liquid extracted from the roots of young wheat, produced spontaneously and simultaneously double ovate vesicles, or cells, such as are found in the roots themselves; and in that liquid, though hermetically sealed in glass tubes, the formation of these vesicles or cells was as active after six months as in the liquid freshly taken from the young plant. Mr. Osborne believed these vesicles to be the earliest organisms of plant life, and that this is the direct and prevailing mode of production of the embryo. This accords with the observations of Messrs. Wenham and Devey.
Many other very remarkable plants belonging to the Monocotyledons might be mentioned, as the Dracæna Draco, or Dragon tree of Teneriffe, one of the most ancient trees existing; the Pandanus, or screw pine, with its aërial roots, indigenous in the islands of Oceania; and the Zostera, or sea wrack, the only flower-bearing plant except one that inhabits the ocean; their flowers are minute and bisexual, are rarely produced, but they cover large areas with long grassy leaves. Bulbous plants, and the Orchidaceæ, the most splendid ornaments of our gardens and hothouses, are members of this class. Of the former, the snowdrop, crocus, colchicum, arum, hyacinth, narcissus, tulip, and lily form a group of singular beauty.
A bulb is merely a subterranean stem remaining permanently in the condition of a bud. It consists of a disc, or conical plate, which is the point of growth whence the flower-bearing stem and the leaves spring. These are surrounded by leafy scales of a fleshy character overlapping one another. The Liliaceæ and the Amaryllidaceæ contain many of the most remarkable and beautiful bulbous plants known in gardens. To the former order belong the hyacinth, tulip, and onion, in which the growing point is surrounded by a series of fleshy tunics, each of which encloses its predecessor; as also the lily itself, in the bulb of which the growing point is enclosed in fleshy scales imbricated in rows one above the other. One or two circles of roots descend from the circumference of the disc in the form of slender, soft, white cords or threads, with a spongy termination of cellular tissue to imbibe water and other liquids for the nourishment of the plant. These bulbs are reproduced by buds, or offsets, developed in the axils of the fleshy scales, which fall off either the first or second year of growth. Offsets are also produced by the arum, crocus, and meadow saffron or colchicum, whose bulbs form a solid mass, and are called corms. These offsets merely reproduce a facsimile of the parent. In these and all flowering plants fructification must take place before a new form or variety can be expected.
The Orchids surpass every plant in the vegetable world, for the variety of means employed by nature to continue the race. The blossoms are, for the most part, at once both male and female, though some plants are diœcious, but, except in rare instances, as in that of the Bee Orchis, not a blossom can be fertilized without the aid of insects. The flowers of the Orchideæ are constructed upon a fixed plan, which can be traced through the innumerable variety of beautiful, singular, and often grotesque forms which they assume. A corresponding variety is exhibited in the admirable contrivances and adaptations which enable insects to detach the pollen from one blossom, and carry it to fertilize another blossom.
Fig. 72. Orchis mascula:—A, side view of flower, with a portion cut away; B, section through one side of rostellum, with included disc and caudicle of pollinium; a, anther; r, rostellum; d, disc.
The British Orchideæ belong mainly to three natural groups: the Ophreæ, which comprise the Orchis, Ophrys, and other common Orchids; the Neotteæ, comprising Epipactis, Neottia, Spiranthes, &c.; and the Malaxeæ, represented by Malaxis. Orchids have white, fibrous roots, and many of them a pair of fleshy tubercles. From thence a straight stem springs up, ending in a spike of blossoms, each of which is attached to the stem by a twisted stalk, containing the ovarium, as represented in [fig. 72]. Ribbed lanceolate leaves rise from the roots, and some are attached sparingly to alternate sides of the stem. The calyx is formed of three pointed sepals, one perpendicular, the others horizontal. Instead of being green they are usually coloured. Sometimes the whole plant is green. One petal ([fig. 72]) is much larger than the others, occasionally assuming the most extraordinary forms. It is called the labellum, or lower lip; it secretes nectar, a sweet juice, to attract insects, and is often produced into a long, hollow, spur-like nectary, as in [fig. 72] n. On that side of the spur which is opposite to the labellum, the organs of reproduction are so placed, that an insect alighting upon the labellum cannot insert its proboscis into the nectary tube to eat the honey, without touching them.
Fig. 73. Orchis mascula:—Front view of flower, with sepals and petals removed; a, anther; r, rostellum; s, stigma; l, labellum.
Mr. Darwin, in his admirable work on the ‘Fertilization of Orchids,’ assumes the Orchis mascula as a type for explaining the mechanism of the reproductive organs of the Orchidaceæ generally. [Fig. 73] represents a front view of the flower with all the sepals and petals cut off, except the labellum, or lip; and [fig. 72] is a side view of the same, with the near half of the labellum cut away, as well as the upper portion of the near side of the nectary, or spur.