10 HORTICULTURE FOR SCHOOLS 



14. Dominant and recessive characters. The white char- 

 acter in the above illustration disappeared in the first hybrid 

 generation, and reappeared in succeeding generations. It is, 

 therefore, said to be a recessive character, while the purple is 

 spoken of as dominant. This behavior of characters is not 

 confined to colors of blossoms of the pea. It is a fundamental 

 consideration in all plant improvement through hybridization. 



15. De Vries. Hugo de Vries (born 1848), a Dutch bota- 

 nist, was one of the discoverers in 1900 of Mendel's epoch- 

 making treatise on hybridization. De Vries became professor 

 of plant anatomy and physiology at the University of Amster- 

 dam, in Holland, in 1878. His many important contributions 

 to the study of plant-breeding have stimulated some of the 

 most important investigations since Darwin. 



16. The mutation theory. With the name of de Vries is 

 associated the " theory of mutation," first set forth by him in 

 a book with that title in 1901. Darwin thought that changes 

 are gradual, almost imperceptible, but that any change, no 

 matter how slight, may give a plant an advantage which 

 would enable it to survive in larger numbers than its less 

 fortunate neighbors. De Vries proved by experimental evi- 

 dence that sometimes changes occur, not gradually, but 

 suddenly, or "by jumps." These changes are called mutations. 



These mutations are manifest in many forms. They have 

 been observed in the case of beans as a change in the shape 

 of the seed or as an increase in the plant's resistance to 

 frost. On peach trees, branches have developed which bore 

 nectarines. In carnations and chrysanthemums, as in many 

 other garden plants, sports are often found. Sometimes 

 these mutations give rise to forms useful to man, some- 

 times the reverse. They constitute one of the factors which 

 must be taken into account in any consideration of plant 

 improvement. 



17. Plant improvement a division of science. The 

 subject of plant improvement is so important that it is re- 



