III.KKDiTY AND EVOLUTION IN PLANTS 



3- The difference in the color of the seed-coat (white 

 vs. gray, gray-brown, leather-brown, with or without violet 

 spotting, etc.). 



4. The difference in the form of the ripe pods (deeply 



constricted between the seeds and 

 more or less wrinkled, or the 

 opposite). 



5. The difference in the color 

 of the unripe pods (light or dark 

 green vs. vivid yellow). 



6. The difference in the posi- 

 tion of the flowers (i.e., axial vs. 

 terminal, on normal vs. fasciated 

 stems). 



7. The difference in the length 

 of the stem (the extremes chosen 

 were "tails" 6 to 7 feet, and 

 "dwarfs" ^ feet to i 1 -?' feet in 

 height). 



48. Artificial Hybridizing.- 

 The edible pea is commonly self- 

 fertilized; therefore, to make 

 crosses it is necessary carefully to 

 remove the stamens of one flower 



FlG. 40. Method of pro- 

 tecting flowers from foreign before the anthers have begun to 

 pollen by paper bags, in shed their pollen, and then place 



plant-breeding experiments. u f another flower on the 



(After O.E. White.) 



stigma. I he flowers must then 



be carefully guarded, e.g., by tying paper bags over them 

 (Fig. 40), to prevent other pollen being deposited by 

 insects or otherwise. In this way the experimenter 

 knows just what characteristics enter into the hybrid. 



