DECAY AND DEATH. 135 



be partial and gradual or immediate and complete. Sudden 

 death, or death by violence, results from the injuries in- 

 flicted by too high or too low a temperature, electric shocks, 

 sunstroke, strong corrosives, and the like. These destroy 

 life by disorganising the protoplasm, breaking up the tissues, 

 and arresting the natural movements, and cause death by 

 destroying the machinery or paralysing its action. The 

 gradual effects produced by such injurious agencies as 

 noxious vapours from kilns or factories, or as insects, or 

 parasitic fungi are the same as those produced by starva- 

 tion or suffocation. In the neighbourhood 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 conduce to the death of plants quite as much 

 as the direct injury caused by noxious vapours. A perusal 

 of the foregoing 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 

 aeration, or from the presence of really poisonous in- 

 gredients. If the cause is widespread, so as to involve a 

 majority or the whole of the roots, the consequences are 

 proportionately serious ; if only a few are affected, the 



