120 Heredity and Ei(geuics 



that the flowers may be castrated at the correct time without 

 injur}' and properly protected from foreign pollination until 

 the time for hybridizing. Third, care must be exercised in 

 apph'ing the pollen of the proposed male parent, for both 

 premature and delayed pollination inhibits seed formation. 



The precise conditions under wliich a cross should be 

 made to be the most successful are not easily determined. 

 The proper preparation of the breeding plot even before 

 the plants are grown is necessary. One takes it for granted 

 that on most soils some fertilizer will be used, for the plants 

 must be normal to seed well. The three essential elements 

 of soil fertilit)' are nitrogen, potassium, and phosphorus, 

 and to get the best results compounds of these elements 

 must be present in proper proportions. First, available 

 potassium must be present in rjuantities sufficient for the 

 normal production of healthy roots, leaves, and stems, and 

 a moderate excess will not be harmful. If nitrates are 

 present in excess, however, vegetative growth will be over- 

 stimulated and seed production will be small. A lack of 

 phosphorus will produce the same effect upon seed pro- 

 duction, but for a different reason. Phosphorus is an essen- 

 tial constituent of the proteid compounds found in large 

 quantities in the seed. If the plants are to be in the best 

 condition for the production of good seed after crossing, 

 therefore, the soil should contain just the right amount of 

 nitrates for a normal vegetative growth, and a generous 

 supply of potash and phosphates. The exact amounts 

 must be determined by experiment for each soil and each 

 species of plant. 



External conditions that are also under partial control 

 of the breeder are available moisture through irrigation and 

 sunlight by ])ro])er spacing or artificial shading. 



