320 PRINCIPI-ES OF GARDENING. [CH. IX. 



Some plants like some animals are able to endiu'e 

 a veiy higb degree of temperatiire. Sir Joseph 

 Banks and others have breathed for many minutes 

 in an atmosphere hot enough to cook eggs, and I 

 have myself travelled in Bengal breathing air with- 

 out inconvenience, which rendered the silver mount- 

 ings of my green spectacles too hot to be bonie 

 without their occasional removal. So do certain 

 plants flourish in hot water springs of which the 

 temperature varies between the scalding heats of 

 from 150° to 180° of Fahrenheit's thermometer, and 

 others have been found growing freely on the edge 

 of volcanoes in an atmosphere heated above the 

 boiling point of water. Indeed it is quite certain 

 that most plants will better bear for a short time an 

 elevated temperature which, if long continued, would 

 destroy them, than they can a low temperature. 

 Thus a temperature much above the freezing point 

 of water to orchidaceous and other tropical plants 

 is generally fatal if endui'ed by them for only a few 

 minutes, whereas a considerable elevation above a 

 salutaiy temperature is rarely injurious to plants. 

 But this is not universally the case, for the elegant 

 Pnmula marginata is so impatient of heat, that 

 although just about to bloom, it never opens a bud if 

 brought into a room in which there is a fire. 



Plants, generally, have the power of preventing 

 tlieir sap attaining to the unnatural elevation of 



