DECAY AND DEATH. 127 
From a physiological point of view death may result 
from starvation or from suffocation ; the process in each 
case may be partial and gradual or immediate and com- 
plete. Sudden death, or death by violence, results from 
the injuries inflicted by too high or too low a tempera- 
ture, electric shocks, sunstroke, strong corrosives, and 
the like. These destroy life by disorganizing the pro- 
toplasm, breaking up the tissues, and arresting the 
natural movements, and cause death by destroying the 
machinery or paralyzing its action. The gradual effects 
produced by such injurious agencies as noxious vapors 
‘from kilns or factories, or as insects, or parasitic fungi 
are the same as those produced by starvation or suffoca- 
tion. In the neighborhood of towns it may happen that 
the relative absence of oxygen, or, what comes to the 
same thing, the inability to use what there is, may con- 
duce to the.death of plants quite as much as the direct 
injury caused by noxious vapors. A perusal of the fore- 
going chapters as to the food and growth of plants will 
‘suffice to show why plants die ; and a consideration of 
their life-history as here set forth will show how the 
cause that may kill at one stage of active growth may be 
all but harmless at another stage of growth (see p. 64). 
Death beginning at the Root.—When death begins at 
the root, the supply of water and of the air and food de- 
rived from the soil is cut off, and the plant ultimately 
perishes of starvation. Death at the root may result 
from injury inflicted by small parasitic worms, insects, 
rats, or other creatures—from unsuitable conditions of 
soil, too much or too little water, deficient drainage, 
deficient aération, or from the presence of really poison- 
ous ingredients. If the cause is widespread, so as to in- 
volve a majority or the whole of the roots, the conse- 
quences are proportionately serious ; if only a few are af- 
fected, the plant may not be visibly or materially injured, 
