LEAVES 



107 



somewhat to the Icnticcls to be found in )-oung 

 tree-stems, onl)' those are s(jlel)' for tlie admission 

 of air, while these h'ttle mouths are to let in and 

 out not onl\' air, hut water, xapour, and ox)-f^en. 



These stomata look like little crescent-sliai)ed 

 slits with a curved cell on either side, and as 

 they ciu'xe more or less, the mouths are opened 

 or shut as the plant may require. These little 

 mouths play a very important 

 part in the economy of the leaf, 

 and they exist in immense quan- 

 tities on its under surface. 



It has been calculated that a 

 million stomata exist on a single 

 leaf of the lime tree. When the 

 root has taken up more moisture than is required, 

 then it is the office of these pores, or stomata, in 

 the leaf to c,nve out this extra water in the form 

 of vapour, and we can thus see how the action of 

 leaves must influence climate. If forests are reck- 

 lessly cut down, the bare countr}-, with no foliage 

 to throw moisture into the air, ma)' become an 

 almost barren de.sert, and again in marshy places, 

 where the air is too damp, a wise reduction in the 



STOMATA. 



