Plants of the World
Although much of the astonishing flora of Asia that can be grown in temperate climates comes from areas that are now out of reach, other districts still provide British collectors with rewards. A number of plants from the cooler parts of South Africa, particularly some of the dazzling, have been introduced or reintroduced.
The enthusiasm of alpine gardeners and growers ofhas caused several collectors to visit the lands lying in or round the Mediterranean. They have not brought back many spectacular plants, but those that they have collected are particularly suited to the small garden: charming cyclamens, narcissi, snow-drops, , and . Peter Davis has been honoured by the Royal Horticultural Society for his work in eastern Europe and the Middle East. Oleg Polunin has worked in the Near East. Two great authorities on . Patrick Synge and Paul Furse, have visited Turkey and northern Iran.
New plants have come from North and South America. The rich flora of California and the Rockies continues to provide novelties. From wind-swept Patagonia, Mrs. Ruth Tweedie has brought back several plants that promise well, including a blueand a scarlet ourisia.
Nor should the ardent band of amateurs be forgotten. Helped by immense improvements in transport and armed with appropriate permits, they return from their holidays with gems collected in the mountainous regions of Europe, and in the Middle East.
MUTANTS AND HYBRIDS
Apart from the great diversity of plants that have been collected from many countries, and which have settled happily in the British Isles, others have evolved — first the singular variations that on rare occasions occur naturally, sometimes producing a plant that is much more desirable than the standard type; and second, variations produced by man.
In the first case, a change takes place within the plant — a mutation — causing an obvious exterior change. These mutations occur very infrequently, and even then usually pass unnoticed, for, as mutants are usually so abnormal as to be weakly, Nature soon eliminates them and they disappear.
A good example of one type of mutant is the florist’s double flower — perhaps aor a . Something occurs to an individual plant which causes the stamens (which carry the anthers and the pollen necessary for fertilization) to turn into rather distorted petals. These are quite sterile and useless for perpetuating the plant by seed, particularly as the style (an essential part of the female or seed-bearing part of the flower) is also frequently petal-like. These abnormalities can easily be seen by examining a double flower.
Other mutants are the occasional white-flowered form of a plant that is normally some other colour, or the shoot of a bush rose that unexpectedly begins to climb. From time immemorial observant gardeners have noticed these peculiarities, particularly in food plants when some change has resulted in more food-producing growth, and they have nurtured and propagated this growth by one of the numerous means available to man but not found in Nature, such as the rooting of, grafting, and budding.
Until recent times man had been unable to produce these ‘sports’ as they are called. Now, however, he can do so to some extent.
One method is by the use of a substance called colchicine, found in the autumn( ). Atomic radiation may also have the same effect. But such methods are very haphazard. Often the embryo plant under treatment is killed, and many of the mutants that do result are useless.
The second method of producing new plants occurs sparingly in Nature, but has been used by man on an enormous scale particularly during the last century. If pollen is taken from one kind of plant and placed on the seed-producing organs of another, the seedling, or hybrid, will have qualities that differ from both its parents.
There are, of course, very severe limitations on the production of hybrids. The parents must be closely related members of the same flower family. It is often possible to hybridize, or ‘cross’, two kinds of rose, but a rose could never be crossed with a holly or a lupin.
Hybrids can occur naturally when two kinds of plant grow close together, are compatible with one another, flower at the same time, and, flies or wind carry the pollen at an appropriate time from one to the other. The London plane tree is a particularly famous example of the almost infinite possibilities of producing new plants, for, strange as it may seem, one parent comes from the New World and the other from the Old. It seems certain that at some time an American plane was placed close to an Oriental plane. The wind carried the pollen of one to the female flowers of the other. The seedlings from this union varied from their parents and, probably in the 17th century, were brought to England and planted. The trees proved to be ideal for growing in smoky London.
No one knows how, when or by whom the first London plane tree was produced, though botanists have now proved conclusively that it does unite in its cells elements drawn from an American tree with those from one restricted to Europe and Asia.
Very many hybrids owe their origins to the accidental planting of two varieties of the same family close to one another. For many centuries gardeners unknowingly brought about the necessary conditions by placing plants side by side, and then selected the new plants that arose as seedlings. As far as is known, it was not until the early 18th century that gardeners understood how hybrids arose, and became aware of their power to emulate the process by transferring the pollen themselves.
This was a development of the utmost importance to the human race, for in the hands of scientific breeders plants can be bred to fulfil special conditions — to resist disease, to give bigger and better crops, or to produce more showy flowers. Desirable parents may be brought together from any part of the world, or pollen from an early-flowering plant may be kept alive, by means of refrigeration, for use on a plant that flowers at a different season.
That domestic animals could be purposefully bred had been known for centuries. Now many skilful men took up the work of breeding plants for a specific purpose.
One of the most important was Thomas Andrew Knight (1759-1838), a squire living on the borders of Herefordshire, who was already a skilled breeder of animals. One of the first plants he tackled was the apple, which, although not a native, can be grown to better flavour in England than in any other country.
Knight tackled the job systematically, and, in addition to apples, bred, , , , currants and other plants. But though his practical achievements were great and one or two kinds he raised are still grown, he failed to arrive at the fundamental laws of heredity that lie behind all breeding, possibly because he experimented with too many different plants.
These laws were discovered in 1865 by Johann Mendel, Abbot of Brno, following experiments he began in 1856, using onlyfor his research. Mendel read a paper on his work to the local natural history society, which was duly published, and then forgotten. It was not until 1900, after plant and animal breeders had wasted great energy in experimenting on an ever-increasing scale, that three breeders, searching for information in out-of-the-way scientific literature, came across Mendel’s paper. It was soon published to the world at large, and the scientific study known as genetics was born.
Its immense importance is shown by the fact that there is probably not a single vegetable plant orin today that is not a hybrid. A few are probably accidental in their origins, but the majority are the result of purposeful breeding. Among flowers, almost all roses, , lupins and most annuals have been developed in this way.