DEVELOPMENT OF STORAGE ORGANS: VEGETATIVE REPRODUCTION

Bulbs.

Tulip

The terminal flowering bud with its surrounding leaves in the tulip bulb in the spring of the second year grows above ground, deriving nourishment from the fleshy scale leaves which consequently shrivel up. After the flower has died, the foliage leaves persist, and food is transported from them to an axillary bud which develops into next year ’s bulb. The outermost leaves of such a bud become scales, those next, fleshy, whilst those immediately around its terminal flowering bud will become foliage leaves.

The growing point of the bulb of daffodil and snowdrop is situated on one side of the bulb and persists from year to year, but each year one of its minute axillary buds develops as an inflorescence surrounded by a few foliage leaves. The following year these rapidly grow from the surrounding fleshy leaves. upwards, utilizing food obtained When flowering is over, the foliage leaves persist and transport the food they make to their bases, which thereby become swollen, to serve as food for the parts which will come above ground the following year.

The onion and the wild hyacinth have fleshy leaf bases like narcissus, but each complete bulb grows from an axillary bud of the previous year, I.e. the original growing point lasts only one season.

In all the above cases a new bulb is derived from an axillary bud, so that if more than one bud develops, multiplication is effected. supplied by the rhizome to each ds to become foliage leaves and flowers above ground. Later the axillary buds grow horizontally as food is supplied to them from the foliage leaves, and they become swollen into typical storage rhizomes, each with its terminal bud.

At the end of the season the above-ground portion dies off and leaves a scar. One can tell the age of any part of a rhizome by counting the number of terminal bud scars backwards from a terminal bud. In time the oldest part dies away, leaving a number of separate rhizomes, so that the plant can spread and multiply by this method. Couch grass, nettle and mint spread rapidly by this method although, in these cases, their rhizomes are not typical swollen storage organs.

Corms

The simplest case is that of the crocus or gladiolus corm. In spring a bud at the top of the corm grows upwards with the aid of food from the corm, coming above the surface as a flower surrounded by foliage leaves. When flowering is over, the base of the stem, I.e. just above the old corm, to which the leaf bases are attached becomes swollen with food brought down from the leaves to form a new corm, and one of the axillary buds there also begins to develop. The remains of the old corm persist under the new corm as a dead fibrous mass, whilst the leaf bases die off in autumn and enshroud the new corm with their brown covering. Next year each bud produces a new corm.

In montbretia not all the food in the corm is used up in one season, and the underground portion persists as a string of corms. On the most recent corm an axillary bud may develop as a thin rhizome with a small corm at its end. In these ways extensive spreading and multiplication can slowly occur in both crocus and montbretia.

Tubers

In the Jerusalem artichoke the terminal bud of the tuber becomes the above-ground part of the plant, whilst any axillary buds grow out horizontally to become the new tubers of that season.

The buds in the eyes of a potato develop to become vertical aerial shoots. Where leaves are present on underground parts of the stems of these shoots, the axillary buds there will develop into thin rhizomes growing obliquely. The end of each of these will develop into a tuber during the season. In rare cases an axillary bud above ground will develop into a small green potato, proving the nature of a tuber as a swollen terminal portion of a stem. Since the old tuber rots away, each bud gives rise to a new plant, thereby effecting multiplication.

Tap Roots

We have the true two-year life cycle in the case of tap roots—the second year being occupied with flowering, fruiting and seed dispersal, unaccompanied by vegetative reproduction.

Tuberous Roots

With the approach of autumn the aerial portions of dahlia and lesser celandine die away, although with the latter some leaves persist as a rosette during the winter. Situated between the leaf bases are axillary buds which shoot up the following year, using up the food stored in the tuberous root. Each swollen root has its axillary bud in the lesser celandine, so that vegetative reproduction readily occurs in this case.

Summary

The food stored in plants is thus of great value for rapid growth when conditions are not good enough for rapid photosynthesis, and also enables the plants to carry out vegetative reproduction. The translocation of material is always preceded by digestion of the stored food by means of enzymes, e.g. of cellulose by a cellulase, of starch and inulin by an amylase, of lipidc by a lipase, and of protein by a protease.

Sorry, comments are closed for this post.