186 THE STOKY OF THE PLANTS. 



of flowers and leave them in the sun without 

 water, they fade and dry up in a very short 

 time. We also know that if we forget to water 

 plants in pots, the plants similarly dry up 

 and die after a few hours' exposure. Leaves, 

 in fact, are purposely arranged in most cases 

 so as to encourage a very rapid evaporation ; 

 and evaporation is one of their chief means of 

 \aising water from the roots to the growing and 

 living portions. 



If you examine the under side of a leaf under 

 the microscope, you will find it is covered by 

 hundreds of little pores which look exactly like 

 mouths, and which are guarded by two cells 

 whose resemblance to lips is absurdly obvious. 

 These pores are commonly known to botanists 

 by the awkward name of stomata, which is the 

 Greek for mouths ; and mouths they really are 

 to all external appearance. You must not 

 suppose, however, that they are truly mouths 

 in the sense of being the organs with which the 

 plant eats ; the upper surface of the leaf, as we 

 saw, with its layer of water-cells and its assimila- 

 ting chlorophyll-bodies, really answers in the 

 plant to our mouths and stomachs. The stomata 

 or pores are much more like the openings in 

 the skin by which we perspire ; only perspira- 

 tion or evaporation is an even more important 

 part of life to the plant than.it is to the animal. 

 Each of the stomata opens into an air-cavity ; 

 and through it the liquid evaporated from the 

 cells passes out as vapour into the open air. 

 Many leaves have thousands of such pores on 

 their lower surface ; they may easily be recog- 



