PLANTS INFLUENCED BY THEIR SURROUNDINGS 123 



more easily seenjn the case of heat than in other cases. 

 We all know that too much heat quickly kills both 

 animals and plants. On the other hand, if they have 

 too little, they stop growing and may die. 



The less water the plant contains, the better it resists 

 cold. This is well shown by greenhouse plants; too 

 much water makes them very sensitive to heat and 

 cold and to light as well; such plants are liable to "sun 

 scald." Plants which have just been transplanted are 

 said to be less sensitive to frost, since they contain less 

 water. Frost does not injure buds in winter, when they 

 are quite dry ; but in spring, when they are full of sap, 

 it kills them. 



The way in which a frozen plant is thawed out is 

 very important. Allow some potatoes to freeze (they ( 

 may be easily frozen in a water-tight can, plunged into 

 a mixture of pounded ice and salt, or set in an or- 

 dinary ice-cream freezer). Place some of the frozen 

 potatoes in water chilled by ice (but free from salt), 

 and let them stand until the water reaches room tem- 

 perature. Place others at once in a warm place, so 

 that they will thaw quickly. Note the difference in | 

 the outcome. 



Plants are sometimes protected from frost by cover- 

 ing the plants with a mulch, or, in the case of trees and 

 shrubs, by bending them down (the roots must be cut 

 in such a way as to permit this) in the fall, and covering 

 them with straw or brush. 



