LEAVES I i i 



sunlight. Weigh again the next day. The differ- 

 ence in the two weights will represent the amount 

 of water transpired by the plant. The weighings 

 may be repeated until moisture gives out. If it is 

 desired to continue this experiment some time, a 

 small hole should be cut in the pasteboard before 

 it is fastened to the jar. This hole is for adding 

 water to the jar from time to time. The hole should 

 be kept closed with a cork. The amount of water 

 added should always be weighed and account taken 

 of it in the following weighings. While this plant 

 is growing it will be well to wrap the jar with paper 

 to protect the roots from the light. 



It has been found that the amount of water neces- 

 sary to grow a plant to maturity is equal to from 

 30x3 to 500 times the weight of the plant when dry. 



This gives us an idea of the very great importance 

 of water to plants. 



Experiment. Take a few leaves from a plant of 

 cotton, bean, clover or other plant that has been 

 growing in the sunlight; boil them for a few min- 

 utes to soften the tissues, then place them in alcohol 

 for a day or until the green coloring matter is ex- 

 tracted by the alcohol. Wash the leaves by taking 

 them from the alcohol and putting them in a tum- 

 bler of water. Then put them in saucers in a weak 

 solution of iodine. The leaf will be seen to gradu- 

 ally darken ; this will continue until it becomes dark 

 purple or almost black (Fig. 61). We have already 

 learned that iodine turns starch this color, so we 

 conclude that leaves must contain starch. (Five or 



