552 



STRUCTURE AND LIFE HISTORIES 



2. The difference in the color of the cotyledons (pale 

 or bright yellow, or orange vs. light or dark green). 



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.j axial vs. 

 terminal) . 



7. The difference in the length 

 of the stem (the extremes chosen 

 were ''tails" 6 to 7 feet, and 

 ''dwarfs" % feet to i}i feet in 

 height). 



473. Artificial Hybridizing. — 

 The edible pea is commonly self- 

 fertilized; therefore, to make 

 crosses it is necessary carefully to 

 remove the stamens of one flower 

 before the anthers have begun to shed their pollen, and 

 then place pollen from another flower on the stigma. The 

 flowers must then be carefully guarded, e.g., by tying 

 paper bags over them (Fig. 406), to prevent other pollen 

 being deposited by insects or otherwise. In this way the 

 experimenter knows just what characteristics enter into 



Fig. 406. — Method of pro- 

 tecting flowers from foreign 

 pollen by paper bags, in plant- 

 breeding experiments. (After 

 O. E. White.) 



