STATING THE CASE. 



2^ 



The leaves of plants, however, are by far the 

 busiest and most highly-organised of all their parts. 

 They are built up of cells like other tissues ; but 

 these cells vary both in 

 shape and size. If the 

 under skin of almost any 

 leaf be peeled off and 

 examined under the 

 microscope, we see not 

 only the sinuous outline 

 of each cell, but an im- 

 mense number of mouths, 

 or stoniata^ each provided 



with movable lips. FiG.8.-Under-surfaceofaLeaf(magnifie^^^^ 



■■■ snowing the o tomata, or hreathmg-mouths. 



Every square inch of the 



under surface of a lilac -leaf has nearly a quarter of 

 a million such mouths. If we cut a leaf in section 

 across one of these stomata, under the microscope 



we are able to see the 

 complete mechanism 

 of the structure, and 

 also how atmospheric 

 air gets into the in- 

 terior of leaf- tissue. 



Fig. 9. — Magnified Section of a Leaf, cut across 



a Breathing-mouth, to show the Structure of The OpCningS intO 

 the latter. - . . • 1 1 



this tissue are rightly 

 called " mouths," for they are actually the chief 

 feeding -places of a plant. It is by their means all 

 the carbon is obtained which afterwards is trans- 



