The evening primrose (Oenothera biennis) is very unlike a primrose, except in colour. Here and there a blossom may be seen expanded in the daytime, but the majority of the flowers do not open till six or seven o'clock in the evening, and then they are slightly fragrant (fig. 43).
Equally well known are the varieties of the "marvel of Peru" (Mirabilis jalapa), sometimes called the "four o'clock," although the time for opening is as late as the evening primrose. The "lady of the night" (Mirabilis dichotoma) is probably the original "four o'clock," as it opens earlier, but popular names must not always be applied with rigid exactitude. These are also pleasantly scented.
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Fig. 43.—Evening Primrose (Oenothera biennis).
Nothing can be more beautiful amongst our native wild flowers than a field in which the night-blooming catchfly (Silene noctiflora) grows in abundance. During the day no trace of the plant can be seen, but at seven o'clock in the evening there is a remarkable change. As though called up at the stroke of a fairy wand, the little blossoms, sparkling like gems, are scattered thickly over the ground. Such a sight is not readily forgotten. Let the experience of lovers of flowers expand this theme upon our brief introduction.
There is another aspect of flowers, for which no special provision is made in our arrangement of chapters, but which is of equal interest, and that is the extraordinary form which the floral organs assume in many families of plants. We might denominate such instances as are present to our mind, as the "eccentricities of flowers." The link which unites them to "meteoric flowers" is very slender, but they are closely related to the object of this volume.
The "reason why" such strange forms are assumed cannot always be determined, but in many instances there is an undoubted connection between the form and the object to be attained, namely the fertilisation of the flower. For instance, it has been suggested that the bright patch of colour on the petals of the rhododendron is so placed with reference to the inclination of the stamens, that insects, attracted by the bright colour, and flying directly towards it, must come into contact with the anthers, and disperse the pollen. Dr. Darwin has indicated in his books, and especially in that on the fertilisation of the orchids, how various modifications in the form and structure of flowers are related to the functions they have to perform. He considers that all the so-called "eccentricities" of form in the floral envelopes are useful, or necessary, to the plant. Some very striking illustrations might be adduced in support of this view, which it would be difficult to controvert. It is much more reasonable to assume that the strange forms sometimes met with are designed to overcome some difficulty, or attain some definite purpose, than to regard them as mere vagaries, or freaks of nature, indulged in by chance, or out of mere sportiveness.
There are no plants which can compete successfully with the orchids for singularity of form. They have been termed the "monkeys of the vegetable world," a not very happy designation, for monkeys do not assume fantastic forms, although they may perform fantastic tricks. Some of these plants grow on the ground in the usual manner, others are parasitic on living trees, the most luxuriant and singular are natives of tropical countries. The lower petal, or labellum in particular, is liable to endless variation. In some cases it is slipper-like in form, in others trumpet shaped. Here and there the entire flower resembles an insect, sometimes to such a degree as to have originated a popular name, as suggestive of the resemblance. This is the case in our own bee orchis (Ophrys apifera), not uncommon on chalky downs (fig. 44). In one curious species the appearance is that of a bird on the wing. The "snipe orchis" is just such a flower as in semi-barbarous countries or amongst a superstitious people, would be associated with some mystic legend, as in the case of another orchid, the "Holy Ghost" plant. The horned labellum of a New Guinea orchid (Pachystoma) exhibits another type of irregularity (fig. 46). And the figure of a flower of a species of Dendrobium, a parasitic orchid from New Guinea (fig. 47) will represent a curious form in which two of the strap-shaped, erect petals, resemble the horns of an antelope. The zebra orchis (Oncidium zebrinum) from Venezuela, has white flowers, with violet transverse bars across the petals, and may be characterised rather as singularly beautiful than eccentric.
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Fig. 44.—Bee Orchis (Ophrys apifera).
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Of all genera of orchids none are stranger than that called Masdevallia. The species are designated by such names as "chimera," nycterina, troglodytes, &c., which are justified by their weird and "uncanny" appearance. Description alone could scarce convey an adequate impression of these strange flowers, some with long tails hanging down from the extremity of each petal, others with similar appendages thrust out, more rigidly, in all directions, and all with a sombre hue, suggesting thoughts of gorgons, medusae, and of "hydras and chimeras dire."
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Fig. 47.—Dendrobium D'Albertisii.
The flowers of the family of birthworts are tubular or trumpet-shaped, here and there strangely inflated, lurid in colouring, sometimes foetid in odour, and often of large size; many of them are climbers, and their rugged, contorted stems, with a snake-like form have in many countries a reputation as an antidote to snake-bites.
The asclepiads have regular flowers, often with thick fleshy petals, sometimes resembling wax flowers, and a structure interesting to botanists because of its departure from the ordinary type, the pollen masses being of a similar nature to those of Orchids. Our illustration of a Ceropegia (page 192) exhibits the vase-like shape which those flowers assume, whilst others are much more simple, and scarcely conspicuous.
<!-- image -->Fig. 48.—Zebra Orchis (Oncidium zebrinum).
The "hand plant" of Mexico (Cheirostemon platanoides) has acquired its designation from the stamens being extended like the five fingers of a hand, from a large calyx, like a leather cup, true petals being absent. The flowers secrete a quantity of liquid like sugar and water, tasting and smelling like toast and water. Each flower continues about a fortnight in perfection before it begins to fade. It was narrated of this flower, when first found in 1787, that it was so great an object of curiosity with all the inhabitants of New Spain, that the flowers were gathered with avidity by the Indians, even before their full expansion, and thus the seeds were not allowed to ripen. The tree was venerated from time immemorial by the Indians, who believed it to be a solitary tree, of which no other existed or could exist in the world. Nevertheless other trees were discovered in Guatemala in 1801.
Side-saddle flowers (Sarracenia) are surmounted by a kind of hood, not unlike a parasol, with the petals hanging out, all round the margin, like little saddle-flaps. Of a different character, but no less strange, are the laterally flattened pink flowers of a plant now common in gardens, which first bore the name of "Dutchman's breeches" (Dielytra spectabilis). Some of the tubular flowers are beautiful enough to merit the old belief that they were the habitations of the "good people."
'Twas I that led you thro' the painted meads, Where the light fairies danced upon the flowers, Ranging on every leaf an orient pearl, Which, struck together with the silken wind Of their loose mantles, made a silver chime.
NOTE.—By an unfortunate accident the manuscript of this, and the five or six succeeding chapters, was lost on its way to the printers, and had to be re-written under disadvantages, for the notes and memoranda accumulated during some fifteen years had been incorporated, and the originals destroyed. Undoubtedly some omissions will have to be accounted for by this circumstance.
CHAPTER XIII
HYGROSCOPISM.
HYGROMETRIC and Hygroscopic are two terms which have been applied indiscriminately, or interchangeably, to indicate certain movements in the parts of plants resulting from a susceptibility to dryness or moisture. These phenomena are often exhibited by dead and dried organs, but sometimes during vitality. It is difficult to mark a distinct line between such phenomena as exhibited by dead and living tissue, nor is this essential, since in all cases the causes are similar, and consist in the different size, form, and density of subjacent series of cells, which expand and contract, at different rates, and to diverse extent, by absorption or loss of moisture, thus producing twisting, curving, or contortion in alternate directions. In other words, it may be accounted for "by supposing that the cells on one side are larger, and have thinner walls than those on the other; and these will therefore be most easily distended when placed in water, and will soonest lose their fluid in drying."
One of the oldest and best known illustrations of hygroscopism, is the awn of the wild oat (Avena fatua), which, in times gone by, has been taken advantage of by designing men to impose on the credulous and superstitious. These awns are twisted in their lower portion, and so susceptible of moisture, even that of the human breath, or a damp hand, that they at once exhibit spontaneous movement, twisting and writhing as if endued with animal life. "Jugglers in the good old time predicted events, and told fortunes, from its motions; and, to cover the cheat, they called the awn 'the leg of an Arabian spider,' or 'the leg of an enchanted fly.'" The true rendering of the phenomena, when it came to be understood, supplanted the jugglers. Hooke, one of the early writers on microscopical objects, saw beneath the mystery, for he writes:—"Its sensibility to changes in the atmosphere seems to depend on the different texture of its parts, for the awn is composed of two kinds of substances, one that is very porous, loose, and spongy, into which the watery streams of the air may be very easily forced, which will be thereby swelled and extended in its dimensions; and a second that is more hard and close, into which the water can very little or not at all penetrate, this therefore retaining always very near the same dimensions, and the other stretching and shrinking, according as there is more or less moisture or water in its pores, by reason of the make and shape of the parts the whole body must necessarily unwreath and wreath itself."
<!-- image -->Fig. 49.—Wild oat (Avena fatua).
Another grass, which, although not a native, is often cultivated, has very long awns, which are subject to twisting and writhing under increase or decrease of moisture. The whole structure and mode of action in the awns of this species were made the subject of an elaborate investigation by Mr. Francis Darwin. The seed terminates downwards in a sharp, strong, oblique point, armed with a dense plume of barb-like hairs; upwards it is continued in a strong, woody awn, of which the lower part is strongly twisted on its own axis, and its upper portion untwisted and fringed with a series of beautiful hairs, so as to impart a feathery appearance. It is bent like a knee between the twisted and untwisted portions. When the seed is fixed, and the awn free, moisture applied to it causes the lower portion to untwist, and with it the feathered upper part is carried round, so that the movement is conspicuous. As the moisture evaporates, the twisting of the lower portion of the awn again takes place, and the twisting and untwisting may be repeated at will, as moisture is applied or withheld. If the feathered end of the awn is fixed, and the seed is free, the latter will be carried round, rotating with the movement of the twisting or untwisting awn. The object of the investigations alluded to was to determine what was the reason for this twisting, and what purpose it served in the economy of the plant. Without entering into the details, which may be consulted at will, it may be assumed as proved that the hygrometric property possessed by the awn, whereby it twisted and untwisted, would enable the sharp point at the lower extremity of the seed to penetrate and bury itself in the ground. It was shown by experiment "that the seed was buried, both as it untwists, and also as it returns to a state of torsion. By a combination of these two processes the awn is thrust into the soil to such a depth as to cover up the seed completely." A seed entangled in the branches of a low bush, and left out of doors for eight days, had buried itself to a depth of thirty-one millimetres, or nearly double the length of the seed, impaling a piece of rotten leaf in its way. It was found that seeds dropped from a height of a few feet usually preserved a nearly vertical position, striking the ground with the point. If allowed to fall among low vegetation they become fixed in a more or less oblique position, the seed resting on the ground. The length of the feather renders entanglement easy, and, when a seed is once entangled, the hairs serve to hold it fast and prevent the wind blowing it away.