ciples of breeding to plants, although they have been applied to the breeding of animals for many years. Among the circumstances are the following:

I. Lack of knowledge of the sexuality of plants until recent times.

2. Difficulty of control in breeding plants.

3. The selection is made from seeds which are embryos and not mature individuals.

The last two circumstances apply much more to some plants than to others. They apply with special force to ordinary field crops.

33. Sex. The sexes in animals must have been known from the earliest times. Camerarius first published experimental proof of the sexuality of plants December 28, 1691. It was not until after this discovery that the function of pollen and its necessity to seed formation was understood. It will be readily appreciated that this knowledge did not become general among the growers of the staple crops until much more recent times and is perhaps still not understood by many. Thus there has been more or less systematic breeding of animals for 4000 years, while the mating of plants has not been practiced for more than two hundred years.

34. The Difficulty of Control in Breeding Plants.—The pollen of plants cannot ordinarily be confined, while the male domestic animal can be tied up by a halter or confined in a yard. In some plants like maize which is wind-fertilized we have no knowledge of the plant from which the pollen came and consequently no knowledge of the characteristics of the sire. In other plants like wheat that are self-fertilized two individuals cannot be mated without resorting to artificial means.

35. The Seed an Embryo.-The selection is usually made from the seeds. The seed is an embryo, not a mature individual. The characteristics of the mature chicken cannot be fully foretold by looking at the egg. The seed must be grown

and the plant observed through youth, maturity and old age before the characteristics of the individual plant are fully known. The individual animals are constantly under the eye of the successful breeder. The poorer animals are rejected and only the better animals mated. In the case of plants there is not only usually no mating, but the mature individual from which the embryo is obtained for the subsequent progeny is unknown. This is not quite so true of maize as of the other cereals, because of the method of harvesting the crop. Even if the large ear of maize is a measure of the productiveness of the individual maize plant, the character of the sire is unknown. In the case of the other cereals, or of potatoes, the size of the grain or tuber is no necessary measure of the productiveness of the parent. A small grain from a fine, well-bred individual is better than a large grain from a poor, indifferently-bred individual. Other things equal, a small tuber from a large hill of potatoes is better than a large tuber from a small hill. In case the large and small seeds come from equally good heads of wheat, which will probably be the case under average conditions, the large seeds may perhaps give the best results, especially as under field conditions the larger size may be of advantage in enabling the plant to get a more vigorous start. Specific proof of this is, however, lacking. Hays believes it to be established that the best heads of wheat, as well as best plants, should be selected. In the case of maize the butt and tip grains have been found to be substantially equal to the middle grains of the ear. (272) To succeed in plant breeding the seed must be selected from individuals which possess the characteristics it is desired to perpetuate.

36. Examples of Improvement or Modification in Plants.Many of the modifications which have taken place in plants during cultivation by man may be said to be unconscious. At least there was no definite plan to accomplish the results attained.

A good illustration of unconscious improvement is to be found in cabbage, kale, collard, palm borecale, Brussels sprouts, kohl-rabi, ruta-baga and cauliflower. These all come from a single, somewhat woody, branching perennial (Brassica oleracea L.) which is to be found growing wild on limestone bluffs in southwestern Europe. Some are a modification of the leaf, as in the cabbage and kale, others of the stem, as kohl-rabi, still others of the root, as ruta-baga, while in the cauliflower it is the selection of the inflorescence that has caused the peculiar modification. Some of these types have twenty or thirty varieties, so that there are probably over one hundred distinct forms from this one wild type. All of these forms are the result of long and patient selection of variations that were considered desirable by the gardener without any conscious attempt to produce these specific forms.

37. Examples of Definite Improvement.-The sugar beet is an illustration of systematic breeding to bring about a definite improvement. In less than a hundred years of systematic selection of individuals of known excellence, and by testing their ability to reproduce the desired characters, the common garden beet, with 6 per cent of sugar, has been transformed into the sugar beet, which often contains from 15 to 20 per cent of sugar and is otherwise improved.

By similar methods, wheat, flax, timothy and other farm crops are being systematically bred for definite characters. The proper method to be employed will be discussed under the crop in question. Much greater advance has been made with vegetables and other horticultural crops than with field crops.

"At the present day species that have been cultivated for many years have become, so to say, like wax in the hands of special growers, who mold them and fashion them to their taste, obtaining the various modifications of shape, size, flavor, etc., demanded by their patrons and the caprices of fashion."

The time will doubtless come when there will be many breeders of pure strains of maize, wheat, timothy and other field Henry L. De Vilmorin. E. S. R., Vol. XI, p. 6.

crops, just as there now are many breeders of pure strains of domestic animals.

38. Methods of Improvement.

There are three steps or

methods in the improvement of plants or animals, viz.:

A. Inducing variation.

B. Selection of forms having desired characteristics.

C. Testing the power of specific forms to reproduce themselves.

39.

A. Inducing Variation.-Variation is the basis of selection. Plants must vary or they could not be selected. are two general methods of producing variations, viz.:

I.

There

Environment, such as soil, climate, space, cultivation, etc. 2. Crossing.

40.

The Influence of Environment.-The causes of variability cannot be discussed here, but the following facts should guide the breeders of plants.

1. Horticulturists do take advantage of a superabundance of food in causing modification or multiplication of parts, such as the development of petals from stamens. After this habit becomes fixed it will be transmitted in some measure even in poor soil,

2. Nevertheless the most important value of cultivation in the case of most plants is to allow the plant breeder or cultivator to study individual forms. It enables him to select the desirable forms and reject the undesirable ones. By milking the cow and testing her milk we are able to select the best milkers. By trotting horses we are enabled to breed those best able to trot. Whatever influence milking or trotting may have, the fact remains that it makes possible intelligent selection.

3. The variations selected should be those induced under the environment in which we expect to continue to grow the crop. If we expect to grow three stalks of maize to the hill in general field culture, it is desirable to select the ears for planting from maize grown in a similar manner, rather than from ears

where but one stalk is grown in a hill. In the latter case the size of the ear will not be a criterion of the size of the ear where three stalks are grown in a hill. Where it is not possible to make selection under field conditions, care should be taken to select from among plants under like environment and subsequently subject to field conditions.

"In selecting sugar beets," says Vilmorin,1 "those roots are sought for that are straight, long, and free from lateral branches. This is right, for those that are branched are more difficult, and hence more expensive, to gather. Now, certain growers of beet seed in the north of France once formed the idea-thinking, no doubt, in this way to improve their varieties-of growing the plants which were to be used as seed stocks in very rich deeply worked soil where they were very much crowded together; so much so that 16 to 20, or even more, grew on one square meter of ground. The result was that the beet assumed the form, and later the length of a whipstock. They were not branched because the roots were very closely crowded together. Their sugar content was abnormally high as a result of their growing so close together, and the conclusions drawn from the form of the roots and their sugar content, as determined in the laboratory, were tainted with error because they did not represent qualities truly acquired, but modifications accidentally imposed by external conditions. Thus these beets which were declared to be of good shape and composition in the laboratory yielded seed which when sown in the open field, produced branched roots of only moderate sugar content, because the descendants had reassumed their true characters when they were released from the restraint which had been artificially imposed upon the parent plants."

41. Change of Seed.-A frequent change of seed is not necessarily a good thing; certainly it is not necessary to obtain seed from distant parts of the country for a region whose soil and climate are well suited to the crop. If the region is not well adapted to the crop frequent new supplies of seed may be helpful and even essential. Probably no part of the world is better adapted to maize than is much of the central Mississippi valley. There would seem to be no good reason for changing seed of maize in this region. Much of this same region is not equally well suited for the oat crop. The climate is too hot and dry. The oats are much lighter than those produced in more moist and cool regions. Obtaining seed oats from regions where the crop does better may be good business management. 1 E. S. R., Vol. XI, p. 13.