40 THE STORY OF THE PLANTS. 



carbon and drink water, and, under the influ- 

 ence of sunlight, to take in energy and build 

 them up into living material. 1 *" 



The starch and sugar and other things thus 

 made are afterwards dissolved in the sap, and 

 used by the plant to manufacture new cells and 

 leaves, or to combine with other important mate- 

 rials of which I shall speak hereafter, in order 

 to form fresh living chlorophyll. 



Now we know what leaves are for ; and you 

 can easily see, therefore, that they are by far the 

 most essential and important part of the entire 

 plant. Most plants, in fact, consist of little else 

 than colonies of leaves, together with the flowers 

 which are their reproductive organs. We have 

 next to see Wliat Shapes various Leaves assume, 

 and what are their reasons for doing so. 



The leaf has, as a rule, to be broad and flat, 

 in order to catch as much carbon as possible ; it 

 has also usually to be expanded horizontally to 

 the sunlight, so as to catch and fix it. For this 

 reason, most leaves that can raise themselves 

 freely to the sun and air are flat and horizontal. 

 But in very crowded and overgrown spots, like 

 thickets and hedgerows, the leaves have to fight 

 hard with one another for air and sunlight ; and 

 in such places particular kinds of plants have 

 been developed, with leaves of special forms 

 adapted to the situation. The fittest have 

 survived, and have assumed such shapes as 

 natural selection dictated. 



Where the plants are large and grow freely 

 upward, with plenty of room, the leaves are 



