268 AGRONOMY 



widely aberrant forms are seldom stable. It is better to breed 

 from a plant, all of whose members show some advance along 

 the lines desired, than to breed from one which shows a 

 greater advance in a single member. In breeding for large 

 flowers, for instance, one should select plants in which all the 

 flowers are a little larger, rather than a small-flowered form 

 which may produce one or two superior blossoms. It is also 

 desirable to breed for one thing at a time, or, if more is 

 attempted, to choose characters which will not conflict in 

 developing. 



Roguing. After a form has been developed to a point 

 where its superiority to the common form is apparent, it can- 

 not be depended upon to continue in this state without assist- 

 ance. Left to itself it will soon " run out," that is, it will return 

 to the general average of the type, and the improvement gained 

 by breeding be lost. When the plants have acquired the de- 

 sired form, further variation is undesirable and effort must 

 now be directed to fixing the type. All plants, therefore, that 

 are not close to the ideal form should be destroyed as soon as 

 detected, to prevent the good and bad plants from mixing by 

 pollination. This is called roguing. If one is endeavoring to 

 breed a certain strain of plants, he will sow as many seeds as 

 possible, preserve only the best for subsequent breeding, and 

 destroy the others. 



Xenia. When a cross between two plants is made, any dif- 

 ferences due to the union will not appear until a new genera- 

 tion has been grown from the seeds resulting from the cross. 

 In certain cases, however, the seeds themselves, or even the 

 fruit, may show the effects of crossing. A good illustration 

 may be had in corn, which readily mixes when two sorts are 

 grown together. This effect is known as xenia. Ordinarily, 

 when a plant is fertilized, a single gamete from the pollen tube 

 unites with another in the ovule to form the cell from which 

 the embryo is produced. In cases of xenia another gamete 



