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., 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^ 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 
FIG. 406. Method of pro- 
tecting flowers from foreign 
pollen by paper bags, in plant- 
breeding experiments. (After 
O. E. White.) 
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 
