PLANTS NEED WATER 105 



should be kept clean and open by frequent baths which 

 ought to be taken daily, if possible. 



Dirt cannot be removed completely without the use 

 of soap. There are two kinds of soap laundry soap and 

 toilet soap. Soap which is suitable for washing clothes 

 and for general housecleaning is usually unfit to be used 

 on the skin. On the other hand, toilet soap, which is 

 intended for tender skin, would have little cleaning- 

 power if used on clothes. See Section 77. 



40. Plants Need Water. 



We all know that plants need water, for if we forget 

 to water them they quickly wilt, and, if they go too long 

 without water they die. If the plants have only wilted 

 they soon take up the water and become stiff and vigor- 

 ous again. In the next section we shall learn the reason 

 for this change. The amount of water which plants 

 need is very great. The water is carried away from the 

 leaves by evaporation,] ust as it is carried from wet clothes 

 which are hung to dry. When we think of the very 

 large surface of the leaves of a tree we will realize that 

 the amount of water which can be given off is enormous. 

 We call the giving off of water from the leaves of a 

 plant transpiration. Transpiration takes place only on 

 the under side of leaves. 



Seeds will not begin to open unless they are supplied 

 with water. Then they swell until they burst, and the 

 young plant comes forth. The amount that seeds swell 

 is always a surprise, as you know if you have ever "put 

 beans to soak." 



