USE OF WATER IN PLANTS. . 



from excessive loss of water. To prevent this 

 many leaves have the power of curling them 

 selves up so as to cover the pores (stomata) 

 with the over-arched leaf-blade, thus further 

 reducing evaporation. Many leaves have their 

 pores so placed that when the leaf is curled 

 up during dry weather they are all under 

 cover, none being present on the exposed, 

 outer-side. Thus it will be seen that or< lei- 

 prevails even under such disturbing condi- 

 tions as those which lead to the withering 

 of leaves by drought, when all appears con- 

 fusion. There are many other contrivances 

 for protecting plants from excessive loss of 

 water. Amongst the most common are the 

 thickening of the outer skin well seen in 

 crotons and the various ' dagger ' plants and 

 the provision of a coating of hair, for 

 instance in the geranium and 'cattle- tongue/ 



5. It is important that the pores in the 

 leaf should be enabled to perform their func- 

 tions under all the conditions to which the 

 plant may be exposed. We have already seen 

 how in some plants they are covered and pro- 

 tected during drought. It is also often essen- 

 tial that they should not be readily filled by 

 drops of water during rain or dew and the 

 surfaces of leaves often have slightly waxy or 



