Principles and Methods of Plant-Breeding 



1717 



Hybridization 



Among the higher plants, as well as animals, every individual is the 

 product of the fusion of germ cells from two parents. In other words, 

 plants have sex and are possessed of female organs and male organs. 

 The latter consist of the filaments and anthers of flowers, while the former 

 consist of the style and stigma. The floral parts of timothy shown in 

 Fig. 75 will serve our purpose as an illustration. The anthers produce 

 pollen, which is the male element. Some of this pollen falls on the stigma, 

 and from there it is conducted through the style to the ovary or female 

 element, where fertilization takes place. Fertilization means the process 

 in which the male element unites with the 

 female element. As a result of this union a 

 new individual is formed, or, rather, a seed is 

 formed which will develop into a new indi- 

 vidual. This new individual contains the 

 characters of both parents to a certain extent. 

 The process of crossing one plant on another 

 plant of a different variety or strain is called 

 hybridization. 



It has been found that these characters 

 behave in a definite way, according to Mendel's 

 law. * According to this law, characters behave 

 as units, or single items. The term " unit 

 characters " is often applied in this connection. 

 The character of every individual plant or 

 animal is represented in the germ cell by a 

 small unit. This must be true, since offspring 

 do possess the characteristics of the parents, although nothing except the 

 germ cell is handed on from the parent to the offspring. This law of 

 Mendel includes the laws of dominance, segregation, and recombination of 

 characters, terms which will now be defined. 



Mendel's law may best be explained, perhaps, by referring to the experi- 

 ments that Mendel himself performed. He worked with a tall variety 

 and a dwarf variety of the common garden pea. When he crossed a tall 

 pea with a dwarf, all the plants resulting from this cross were tall. 

 When the seed from these tall plants was planted, it produced both tall 

 and dwarf plants in the ratio of three tall to one dwarf. When the seed 

 from these last tall and dwarf plants was planted, the third year of the 

 experiment, one third of the tall plants produced tall plants; the other 



* This law was formulated by Gregor Mendel, an Austrian monk, in 1865, but remained unnoticed until 

 1900, when it was rediscovered by three men at almost the same time. 



Il8 



Fig. 75. — Drawing of a tim- 

 othy flower, showing the 

 floral parts: a, anther; f, 

 filament; s, stigma; y, style 



