WATER IN PLANTS 19 



you will find that they contain a much larger propor- 

 tion, while a seedling plant may lose on drying as 

 much as ninety per cent of its weight. 



When the water is driven off the leaves wither and 

 shrink, and the stem becomes flabby and weak, just as 

 a bicycle tyre does when the air is let out, and for 

 exactly the same reason. The water in the plant is, 

 as it were, pumped tight, like the air in a bicycle 

 tube, and helps to stiffen the weaker parts, especially 

 the leaves, just as the air in the tyre does. 



To learn how much water a plant actually requires, 

 take a small pot in which is a well-grown COLEUS, 

 CALADIUM, Sunflower or any leafy plant. 



Wrap it round with a thin india-rubber sheet or 

 piece of oiled cloth, tying the sheet round over the 

 top of the pot so that as little as possible of the 

 earth is exposed to the air, and only the shoot itself 

 sticks out. Weigh the whole in the morning, and 

 write the weight down. Weigh it again in the evening; 

 the weight will be less. Add water until it is about 

 the same again and weigh it again, and in the morning, 

 and the next evening and so on. 



You will find that every morning the weight is just 

 a little less than it was after the plant had been 

 watered the evening before, and that at the end of 

 the day it is a good deal less. This shows that water 

 is lost by evaporation, and that much? more is lost 

 during the day than at night ; since the pot and the 

 soil have been covered up by a water-proof sheet, the 

 loss of water must take place through the plant itself. 



Now cut off all the leaves, not the branches, and 

 repeat the experiment. There will now be hardly 



