62 



FIRST STUDIES IN PLANT LIFE 



the water from the root leaves the plant. You see 

 in fig. 36 little doors in the lower skin where the water 

 goes out in the form of vapour. These openings look 

 like mouths, but we shall call them breathing-pores.* 



10. The breathing-pores. Every leaf has many 

 of these openings, and some have many thousands of 

 them. On every square inch of either side of a blue 

 gum leaf there are 22,000 of them. When the plant 

 has plenty of water, the breathing-pores are kept wide 



open, and evaporation 



(L_^ ,\1| y/ goes on quickly ; but in 



■«^^^n^.J|^^^^J|(\_y^ dry weather when the 



n^^^^^^^^^HrHC pl^''^^ needs all its 



^^p^^0y/\^^]r~/'/' moisture, the openings 



•^^^~' ''Vr^^'i— i!-^^ ( — • are closed. In order to 



prevent evaporation 



going on too quickly, 



the breathing-pores are 



in the lower skin. This 



is nearly always the 



case where the leaf holds its upper face to the sun ; 



but in leaves, like the gum tree leaf, that hang 



downwards, both sides have breathing-pores. 



Questions and exercises : — 



(1) Shew how in a tree we have the invisible made \-isible. 



(2) Wood ashes make excellent manure. Why is this? 



(3) Why is it important to keep the leaves of a plant free from 

 dust? 



(4) Early in summer a cherry tree is stripped of its leaves by 

 the pear slug. This hurts the tree in several ways. Mention 

 any. 



(5) How does the elk-horn fern live ? Why does it grow best 

 in a moist air ? 



The lower skin of a leaf showing 

 three breathing-pores. 



* Stomata. 



