Читать книгу The Book of Bulbs - Arnott Samuel - Страница 2

Anyone who has observed ever so casually the order of flowering of the plants in garden or hedgerow, must have noticed that bulbous plants figure prominently amongst those which flower in the early months of the year. Winter Aconite, Snowdrop, Crocus, Scilla, Chionodoxa, Daffodil, Fritillary, Anemone, and Tulip are among the greatest treasures of the spring garden, and though these are not all strictly bulbous plants, they all have either bulbous, tuberous, or other enlarged form of root or underground stem which serves a like purpose. Even those early flowers, the primroses, are borne on plants whose thick, fleshy, underground parts are almost tuberous in appearance; and it will be found that all the earliest blooming plants of spring are furnished with large stores of nutriment in root or stem. Only by virtue of these granaries of materialised solar energy, accumulated during the spring and summer of the previous year, are plants able to manufacture leaves and beautiful flowers in those early months during which the sun yields little heat and light, so essential to healthy plant life.

In a sense, we may consider bulbs and tubers as functionally equivalent to seeds, for they contain within sundry wrappings a dormant plant and stores of food material, wherewith the young plant may be nourished from the time when growth commences until the plant can fend for itself.

It is easy to understand how great an advantage it may be to a plant, in which cross-fertilisation is essential to racial vigour, to open its flowers before the great armies of floral rivals expose their baits to the gaze of flying insects whose visits are desired. For a like reason, it is advantageous to certain flowers to appear late in autumn after the summer flowers have withered and the competition for insect visitors has abated. These also have usually woody stems, or bulbous or tuberous rhizomes or roots, in which are stored reserves of starch, sugar, and other foods formed in the season of sunlight. Fibrous-rooted plants, on the other hand, for the most part flower between the months of April and September, when the daily hours of sunlight are many.

We commonly speak of the bulbs of crocuses as of tulips or of onions, but morphologically there is a distinction, although functionally there is little or none. If we examine a tulip bulb, we find that it is mainly composed of thick succulent scales which closely overlap one another, in the centre being a flattish axis continuous with the roots below, and with the leaf and flower-bearing stalk above. This axis is part of the tulip's stem, the fleshy scales being morphologically but modified leaves whose basal portions have become swollen with stores of nutriment. After the tulip has flowered, it sets to work to manufacture fresh supplies of food material which is sent down the stem and there accumulated in a new bulb, formed by the development of a bud contained among the scales of the old and now withered bulb of the previous year. These stores will, in the following season, enable the tulip to cut a pretty figure before it or other plant has had time or opportunity for preparing fresh supplies by the aid of the spring-time sun alone.

The so-called bulb of the crocus has a somewhat different structure. The crocus "bulb" does not, like that of the tulip, consist of overlapping scales, but of a more or less homogeneous mass enclosed in a stiff membrane, within which may sometimes be seen two or three smaller membranes of similar structure. From the lower part of the "bulb" issue roots, and from its summit proceed the leaf-bearing and flower-bearing shoots. The crocus "bulb" is not strictly what botanists call a bulb, but is a corm (Κορμος = a stem), the expansion being composed of the swollen base of the stem and not, as with true bulbs, of the leaves – the latter having degenerated into mere membranous sheaths, which have no function beyond serving as protective envelopes for the food store and living nucleus within. As in the case of the tulip, so the crocus, having flowered in the early days of the year, proceeds to make and store up fresh supplies of starch and other food in readiness for the following year. The base of the stem enlarges above the old and withering corm, from which it sucks the remaining nutriment. Fresh roots are formed, some of which, having penetrated the soil to a varying depth, contract in length, and so draw down the new corm to the level of the old.

This contractile power of roots has another office of great interest in connection with bulbs and corms. I have said that new bulbs form around the old exhausted ones by the development of buds in the axils of the leaf scales. It is obvious that in this way overcrowding must result, and that the young bulbs must often fare badly through being obliged to seek nourishment from soil already half exhausted of the elements necessary for the plants' health. But by the development of lateral roots which subsequently contract, such bulbs are often pulled to an appreciable distance from their parent, and thus gradually by yearly steps spread over a considerable area. Kerner quotes an interesting illustration of this process. Some soil containing bulbs of Tulipa sylvestris was once put in a garden in Vienna in the middle of a grass plot shaded by maple trees. As the grass was mowed every year before the flowers opened there was no formation of seeds, and the tulips could only multiply by offshoots. After about twenty years, the lawn was covered with tulip leaves, which arose from subterranean bulbs occupying an area ten paces in diameter. Thus, in the time mentioned, the bulbs had spread for about five paces in all directions in consequence of the pull of the contracting roots.

Indeed, the underground life of bulbous plants, both during their more active stages of growth, and in those times mistakenly spoken of as the periods of rest, is full of interest to the careful observer. That curious process of ripening which is essential to the health of nearly all bulbs is itself no merely mechanical change. Each plant has its peculiar time for bursting through the surface of earth, for expanding its first leaves, and for displaying the glory of its first blooms; and any material hastening of these processes by the artificial application of heat means, except in a few species, subsequent debility to the plant, and, as a rule (though not invariably), diminished character in the flowers thus forced. There are, however, plants, such as Lilies of the Valley, to which the so-called resting stage seems of less duration and importance, and it is such flowers which may be forced under carefully arranged conditions with little ill result.

Among our English wild flowering plants, the principal ones furnished with bulbs or corms are to be found in the orders Iridaceæ, Amaryllidaceæ, and Liliaceæ. Included in the former are the very rare purplish flower known as Columna's trichonema, and the doubtfully native Crocus sativus, the autumnal saffron crocus, referred to by Hakluyt at the close of the sixteenth century: "This commodity of Saffron groweth fifty miles from Tripoli, in Syria, on an high hyll, called in those parts Gasian, so as there you may learn at that part of Tripoli the value of the pound, the goodnesse of it, and the places of the vent. But it is said that from that hyll there passeth yerely of that commodity fifteen moiles laden, and that those regions notwithstanding lacke sufficiency of that commodity. But if a vent might be found, men would in Essex (about Saffron Walden), and in Cambridgeshire, revive the trade for the benefit of the setting of the poore on worke. So would they do in Herefordshire, by Wales, where the best of all England is, in which place the soil yields the wilde Saffron commonly, which showeth the natural inclination of the same soile to the bearing of the right Saffron, if the soile be manured and that way employed."

The Amaryllis order contains the Daffodil and the Snowdrop, as well as Leucojum æstivum, which is thought by some to be a native species. It is, however, the order of the Liliaceæ to which belong the majority of English bulbous flowering plants. Bluebells, like "heavens upbreaking through the earth," purple Fritillaries, yellow Tulips, Stars of Bethlehem with curious greenish flowers, Vernal Scillas, the not-so-pretty S. autumnalis, and the Broad-leaved Garlic, whose white flowers are among the most beautiful of all, though the scent of the whole plant is very "grosse and very unpleasant for fayre ladies and tender lily rose colloured damsels which often time profereth sweet breathes before gentle wordes." There are a few other British bulbous and cormous plants scattered among the various orders, such as the Meadow-saffron which is still used in pharmacy, but the greater number are contained in the three orders named.