V" ON PLANTS. 107 



1*4 



ces of plants, as it does those of the animal frame ; but 

 this effect varies in different species of plants, and even 

 in different individuals of the same kind. It is the accel- 

 erated motion of the sap, during the warmth of spring, 

 which determines .the period of the budding of the plant; 

 and, as the temperature of the season increases, produ- 

 ces a greater absorption by the roots, of evaporation by 

 the leaves, developes the blossom, and, finally, ripens 

 the fruit. 



The action of heat in these operations is not merely 

 mechanical, but produces effects on the living plant very 

 analogous to those which it does on animals. 



When, on the contrary, the temperature of the soil is 

 as low as the freezing point, the spongioles finding no 

 fluid to imbibe, the plant, deprived of sustenance, lan- 

 guishes ; and, should this privation continue any length 

 of time, it perishes of famine. 



Emily. And if the heat be so intense as to evaporate 

 all the water of the soil, the plant will be equally depriv- 

 ed of nourishment. 



Mrs. B. The effect is similar, though produced by 

 so opposite a cause. The plant will in the last case, 

 however, perish sooner ; for, besides being deprived of 

 sustenance, it will evaporate its own moisture. But let 

 us first inquire into the effects of a low temperature on 

 plants. Water may freeze within a plant, but it is less 

 liable to congelation after, than before being absorbed by 

 the roots ; not only because it is better sheltered from 

 the external cold, but because the motion of the sap is 

 unfavorable to congelation. 



If the stem of a tree freezes, the elasticity of the ves- 

 sels requisite for the circulation of the juices is destroy- 

 ed, and the plant perishes both from cold and hunger. 

 But if merely the leaves and buds be frozen, they alone 

 are destroyed ; and the sap, which the stem continues 

 to transmit to the branches, enables them to sprout out 

 new buds and fresh leaves. 



Caroline. So, a man would still live, were his nose or 



600. What determines the period of budding! 601. To what is 

 the action of heat in these operations analogous! 602. When the 

 temperature of the soil is as low as freezing point, what is the conse- 

 quence 1 ? 603. When the heat is so intense as to evaporate all the 

 water of the soil, what will be the consequence! 604. Why is watei 

 within the plant less liable to congelation than before it was absorbed! 

 605. When plants freeze what is the consecmence. 



