388 
SOME GENERAL PLANT PROBLEMS 
which gets rid of the grasses on which it grows; planting 
early varieties of grain which mature before the rust has 
time to develop; planting varieties which have been found 
able to resist the disease ; and, best of all, getting rid of the 
common barberry. Denmark, which eradicated the bar¬ 
berry in 1903, has not had an epidemic of rust since. 
Note. — The Japanese barberry, more commonly planted 
for ornament than the common barberry, is immune to the 
rust, and may be spared. 
320. Plant Breeding. — Plant breeding is a general term for 
the various methods employed to improve a given variety 
Figure 356. — Variations in Yields of Good Seed Corn from Rows 
Planted with Seed from Two Different Ears. 
Crate on left, row 18, 19 pounds seed corn ; crate on right, row 11, 62 
pounds seed corn. Good seed corn worth three dollars per bushel in the ear. 
Only the ears from the high yielding rows are retained as seed corn for 
further experiments. 
of plants. It is well known that there is a wide range of 
variation (page 390) in plants as they grow in a field. In 
the case of food-plants, it is desirable to know the conditions 
which enable a plant to produce the most food. We are 
just beginning to understand some of the reasons why one 
plant is large and another small, why one plant gives a large 
