124 PLANT LIFE ON THE FARM. 
instructions here as to the way in which cross-breeding 
may be carried out; it is difficult with cereals, less so 
with leguminous plants, easiest with the cabbage tribe. 
Indeed, as growers know io their cost, it is difficult to 
keep the races or strains of the cabbage-tribe pure and 
uncontaminated, owing to the facility with which the 
flowers are fertilized by insects which bring the pollen 
from the flower of some other variety. Too high breed- 
ing, however, often entails a delicacy of constitution or 
a defective productiveness which may be overcome by a 
fresh cross with a stronger strain. 
CHAPTER IX, 
DECAY AND DEATH, 
Change, waste and repair.-Disturbance of the balance.—Death of the 
protoplasm.—Causes of death.—Natural death.—How plants die: 
impaired nutrition, starvation, suffocation, structural injury and 
paralysis.—Death beginnjng at the root.—Death beginning at the 
leaf. 
Decay and Peath.—Life is one continual series of 
changes— 
“By ceaseless action all that is subsists.” 
The result of these changes is gain or loss, waste or 
repair, now one, now the other; or occasionally (and 
indeed generally) both simultaneously. While a proper 
balance and equitable adjustment between gain and loss 
exists, the plant lives and is healthy. Directly the bal- 
ance is disturbed the plant may live indeed, but it be- 
comes unhealthy; and if the disturbance continue—itf 
waste overtake repair—if nutrition be persistently im- 
paired, still more if it be arrested, the plant inevitably 
