SOME OP THE PRINCIPLES OP PLANT- BREEDING 



57 



the foliage and it catches the fruit when it falls. When the cross is made, a label or tag is secured to 

 the flower or branch to identify it. 



It is seldom that all crosses " take." The proportion of successes depends somewhat on the skill of 

 the operator and very largely on the kind of plant. Some plants cross very readily and some with 

 great difficulty. 



The seeds are now to be sown. The hybridizer always anticipates satisfaction with the results. 



SOME OF THE PRINCIPLES OF PLANT- 

 BREEDING 



By Herbert J. Webber 



We are inclined to think that plant -breeding is 

 based on old and well-established laws. The fact is, 

 however, that the fundamental principles of plant- 

 breeding were not made known until the latter 

 part of the eighteenth century. The sexuality of 

 plants was established experimentally by Camera- 

 rius in 1691, and the first hybrid of which we have 

 any record was made by Thomas Fairchild, an 

 English gardener, in 1719, being a cross of the 

 carnation with the sweet william. Hybrids were 

 carefully studied by Koelreuter, but not from a 

 practical breeding standpoint. Plant-breeding had 

 its real beginning with the work of Thomas Andrew 

 Knight, an eminent English plant physiologist, 

 working in the early days of the nineteenth cen- 

 tury. About the same time Van Mons, a Belgian 

 horticulturist, also carried out experiments in a 

 similar direction. A large part of our knowledge 

 of plant-breeding has come down to us from 

 these two investigators. Knight worked mainly in 

 hybridization, and in 1806 said : " New varieties 

 of every species of fruit will generally be better 

 obtained by introducing the farina of one variety 

 of pollen into the blossoms of another than by 

 propagating from a single kind." Knight also 

 enunciated what we may call the law of food sup- 

 ply, which is now generally recognized. This pred- 

 icates that one of the principal factors which 

 causes or induces variation in plants is an increase 

 of food supply or a modification thereof. Van 

 Mons worked mainly in selection, and it is inter- 

 esting to note that his experiments were carried 

 out primarily with pears. He preached the doctrine 

 of continuous selection, and produced very many 

 valuable varieties. Van Mons and Knight, there- 

 fore, were the exponents of the important factors 

 of selection and hybridization in plant -improve- 

 ment. It is probable that a large part of the suc- 

 cess of Van Mons' work was due to the fact that 

 pears are normally sterile to their own pollen, 

 requiring cross-fertilization, and, therefore, many 

 of his new varieties were probably hybrids. He 

 (vas not aware of this fact, however, and it made 

 no great difference in the establishment of the prin- 

 ciple which has since proved to be so important. _ 



In this country very valuable work was done in 

 the improvement of plants and in discovering the 

 principles of plant-breeding, by Carman, Pringle, 

 Hovey, Ricketts, Rogers, and others, and in more 

 recent years by Burbank, Hopkins, Hays, Bailey, 

 and very many others. 



The rediscovery of Mendel's now famous law by 

 DeVries and Correns, in 1900, and the publication 



of DeVries' Mutation Theory in the same year, 

 marked the beginning of a new era in plant-breed- 

 ing. No matter what the final conclusions may be 

 regarding Mendel's principles and the mutation 

 theory, the general attention and investigation 

 directed to plant-breeding as the result of these 

 two theories will serve greatly to modify and 

 extend our understanding of the general laws of 

 breeding. 



Classification of varieties. 



To understand clearly the character of organisms 

 with which we are dealing, we need careful defini- 

 tions of the different groups of cultivated plants 

 which are ordinarily known as varieties. We speak 

 of varieties of wheat, corn, apples and pears, yet 

 we know that these varieties differ from each other 

 as natural groups. In order to distinguish clearly 

 these differences, the writer has proposed the fol- 

 lowing classification of varieties into races, strains 

 and clons : 



Races are groups of cultivated plants which have 

 well-marked differentiating characters, and propa- 

 gate true to seed except for simple individual vari- 

 ations. The different groups of beans, peas, wheat, 

 oats, corn, cotton, and the like, referred to com- 

 monly as varieties, are thus in a more restricted 

 sense races. Boone County White, Leaming, Reid's 

 Yellow Dent, and the like, would be recognized as 

 races of field corn, and Turkey Red, Pulcaster, 

 Fultz, and the like, as races of wheat. 



Strains, the writer would recognize as groups of 

 cultivated plants, derived from a race, which do 

 not differ from the original of the race in visible 

 taxonomic characters. When the breeder, by a 

 careful selection of Blue Stem wheat, produces a 

 sort of Blue Stem that differs from the original 

 race only in the quality of yielding heavily, it would 

 be called a strain of Blue Stem. 



Clons are groups of cultivated plants, the different 

 individuals of which are simply transplanted parts 

 of the same individual, the reproduction being by 

 the use of vegetative parts such as bulbs, tubers, 

 buds, grafts, cuttings, runners, and the like. The 

 various sorts of apples, potatoes, strawberries, 

 chrysanthemums, and so on, commonly denominated 

 varieties, in a more restricted sense would be clons. 

 Clons of apples, pears, strawberries, potatoes, and 

 the like, do not propagate true to seed, while this is 

 one of the most important characters of races and 

 strains of wheat, corn, and the like. The term 

 variety would thus be used in a general sense, and 

 would include races, strains and clons. 



■Factors of breeding. 



Heredity. — The laws of heredity are of primary 

 importance to the breeder. It is a general principle 



