Seeds

The successful propagation of plants from ■■• rds is a highly improbable process con-i lering the vast number of seeds produced l>y the parent plant and the relatively small number of plants that survive to maturity under natural circumstances. The gardener, therefore, must recognize all the possible limitations to success, and attempt to reduce or eliminate these and so produce an acceptable crop.

Nevertheless, for the gardener, the technique of propagating plants from seed is a very worthwhile and satisfying exercise as it c an be a prolific method of plant production. It is also gratifying to collect the bewildering variety of seeds in the garden without causing injury to the plants—an inevitable consequence of vegetative propagation.

A seed is produced from the fertilization of the female part of a flower by pollen from the male section. Seed is the end product of the sexual process and as such produces a population of plants that exhibit variable characteristics. By a controlled breeding programme, it is possible to eliminate the greater proportion of this variation and produce a population of seedlings that to all intents and purposes are similar. This is the l^usual practice in the production of bedding plants, vegetables and flower crops—that is those plants With a short enough life-cycle to allow an intensive breeding programme. Woody plant seedlings are more variable ecause of their longer life-cycle and their endency to cross-pollinate in their natural habitat.

Seeds are a resting and survival stage in the continuance of a plant's existence. Basically a seed consists of an embryo, which is the young plant at its most immature and in its simplest components; a food supply, which maintains the embryo throughout the resting period and provides the basis for further development when germination gets under way; and a seedcoat, which acts as the protective component. The embryo consists of the young root system, or radicle; the young stem system, or plumule, which carries the seed leaves, or cotyledons (which may be adapted for food storage); and the hypocotyl, which is the junction between the root and shoot system. Examples of different embryos are given below: one has the food stored in the endosperm; the other has the cotyledons adapted for food storage.

embryos are given below: one has the food stored in the endosperm; the other has the cotyledons adapted for food storage.

Hazelnut Cotyledon

cotyledons hypocotyl radicle

Beech Fagus sylvatica x 2.5

cotyledons hypocotyl radicle

Beech Fagus sylvatica x 2.5

Tilia Platyphyllos Seed

cotyledons hypocotyl endosperm

Lime Tilia platyphyllos x 9

cotyledons hypocotyl endosperm

Lime Tilia platyphyllos x 9

that

There are a number of distinctions can be made within seeds as a group.

The enormous variation in the size of seeds will inevitably influence the success with which they are propagated. Large seeds, such as acorns, chestnuts and hazelnuts, are produced in small numbers, germinate satis-

Oak Leaves And Acorns
Oak Quercus rubra x 1

Rhododendron maximum x 24

factorily, and as a general rule establish well. Dust-like seeds, such as those from rhododendrons and lobelia, have a low germination and survival rate.

Seeds also vary greatly in the materials, that they use as food reserves—that is the stored food in the seed. Those plants that store food as carbohydrates, such as elderberries, marigolds and laburnum, are generally stable and long-lived, and will withstand drying. Seeds that store food as fats or oils, for example peony, magnolia and chestnut seeds, deteriorate both with time and drying and so present problems of storage and survival. It is better to allow these seeds to mature on the plant and collect them just before dispersal.

Elderberry Sambucus nigra x 10

Magnolia grandiflora x 2

Survival of drying, however, is not just a function of the stored food; it also reflects the condition of the seedcoat and its ability to protect the seed. Plants, such as willows, with very poorly developed seedcoats survive for only very short periods, while those plants, such as sweet peas, laburnum and lupin, with very hard, impermeable seed-coats usually survive for considerable periods in a wide variety of conditions. The seeds of the Indian lotus (Nelumbo nucifera) are reputed to have retained viability in a peat bog for over one thousand years.

The variation in characteristics of the seed, and more often the fruit, are endless; some seeds and fruits have large wings, hooks or other projections that provide an aid to dispersal, and these can easily be trimmed or rubbed off. The shape of a seed is designed so that, when it is dispersed, it will fall to the ground and lie in the best position for germination. Altering its shape may affect this characteristic, and so, when planting, try not to place a seed upside down. If incorrectly positioned the stem of the germinating seed may produce a kink.

Magnolia grandiflora x 2

Maple Acer platanoides x 3 Commercial seeds

As well as being sold loose in packets, seeds are now available commercially in other forms that make sowing easier and more accurate. Pelleted seeds are coated with decomposable material which disintegrates when in contact with moisture. It is especially convenient to buy small seeds in this form as they are much easier to handle and sow. Seeds can also be purchased evenly spaced on a tape of decomposable paper or plastic. Just cut the tape to the required length and place it in a furrow\ in deep and then cover with soil.

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