386 



LIFE ON THE EARTH 



there is not enough left to provide for the making and 

 transporting of the food, the work of the plant cannot be 

 carried on, and the plant dies. It is on account of this 

 that many plants are especially prepared to retain their 

 water supply. In almost all plants the stomata, or little 

 pores in the leaf through which the water passes out, close 

 up when too much water is being lost. 



In some plants, like the corn, when the root cannot 

 supply sufficient moisture, the leaves curl up and thus 



present less surface for 

 evaporation. In trees 

 like the eucalyptus the 

 leaves hang vertically 

 when the sun gets too 

 bright and present their 

 edges to the sun's rays. 

 Some leaves, like the 

 sage, are especially pre- 

 pared to conserve their 

 moisture by having their 

 surfaces covered with 

 hairs. Others have a 

 waxy covering, as the 

 cabbage and the rubber 

 tree. In some plants the leaves are very small and have 

 few pores, as the greasewood of the desert, and some have 

 done away with leaves altogether, as the cactus. It is 

 because the roots cannot supply sufficient moisture where 

 the ground freezes in the winter that trees having large 

 leaves shed them. Only trees like the pine, whose needle- 

 like, waxy leaves give off almost no moisture, can retain 

 their leaves. 



A SUNFLOWER PLANT 



