154 CHILDREN'S GARDENS 



and packing them closely in a box, and shutting the 

 cover down tightly to keep the heat in. In about 3 

 or 4 days, they will make so much heat that it will be 

 easily felt by the hand being put in the package. The 

 water that is passed out through the leaves of the 

 plant carries off much of this heat, and keeps the 

 plants cool enough to grow. That the water does 

 carry away heat, can be plainly shown to the children, 

 by having them wet one hand, and keep the other 

 hand dry, and then rapidly swing both arms around 

 in the air. They will find that the hand that has been 

 wet, will become dry in a short time by swinging it 

 around, but at the same time, the water that has left 

 the hand, has carried away so much heat, that the hand 

 that was wet, is now very much colder than the hand 

 that was dry. They can then be allowed to take hold 

 of dry stones, boards or tin cans that have been ex- 

 posed to the hot sun, and compare them with the 

 growing leaves of the plants exposed to the same 

 hot sun. They will find that the leaves are very 

 much cooler, and after the previous experiment, will 

 realize that the leaves have been kept cool by the 

 water that carries away the heat. 



According to the age of the children and their 

 grading in school, the teacher can either stop with 

 such simple experiments as these, or can go into fur- 

 ther detail, and consider how much water each differ- 

 ent kind of crop needs each season, and how much 

 heat is required to vaporize water. (Refer to King's 



