90 



EFFECT OF COLD ON PLANTS . 



Effect of a 



slight fall 



of tempera, 



ture on 



plants. 



The life of 

 dependent 



nai causes 



only one of 

 namely the 



insufficient for the purposes of health, or even hurtful 

 to the individual. 



The whole existence of a plant, the resistance 

 which it opposes to the action of the atmospheric 



i i 



oxygen, is most closely connected with the con- 

 tinued support of its vital functions. The mere 

 alternation of day and night makes, in this respect, 

 a great difference. The sinking of the external 

 temperature by a few degrees, causes the leaves to 

 fall in autumn ; and a cold night is followed by the 

 death of many annual plants. 



If we reflect that a plant, in order to protect 

 itself from external causes of disturbance, or to 

 see ^ tne fd which it requires, cannot change its 

 pj ace . that jfcg nO rmal vital functions depend on 

 the simultaneous and combined action of water, of 

 the soil, of the external temperature, and of the 

 hygrometric state of the atmosphere; that is, on 

 four external circumstances ; it is easy to comprehend 

 the disturbance of functions which must occur in 

 the organism in consequence of any change in the 

 mutual relations of so many combined agencies. 

 The state of a plant is a sure indication of equili- 

 brium or of misproportion in the external conditions 

 of its life ; and the dexterity of the accomplished 

 gardener consists exactly in this, that he knows and 

 can establish the just proportion of these conditions 

 for each species of vegetable. Only one of these 

 numerous conditions is in the power of the agricul- 



