THE LEAVES 79 



Danubian reed, a blade of buffalo grass or of prairie- 

 grass. Notice that though there are no side-ribs there 

 is sometimes a distinct mid-rib to make the blade firm. 



3. This is the plan also for all the lilies, 

 and, indeed, for all plants that have only one 

 seed-leaf. Look at a narcissus, a gladiolus, 

 the harbinger of spring, or any other of the 

 bulb-rooting plants among the wild flowers. 

 Leaves on this plan rarely have any leaf-stalk, 

 and they are seldom deeply cut into. 



4. And now if you ask me why the leaf of 

 IllJIil one plant is on one plan, and the leaf of a 



second plant on a different plan, I cannot 

 always tell you ; but the reason can be 

 guessed in some cases. 



5. How light shapes the leaves. Leaves 

 Leaf of a of poud-plauts are generally finely cut or long 

 with oce and ribbon-like if they live under the surface ; 



Beed-leaf. 



but if they live on the surface of the water, 

 like the water-lily, they become broad and are uncut. 

 This may be due to the fact that water shuts off a 

 good deal of light. Experiments show that leaves 

 become narrower as the light upon them is lessened. 

 There is a pond-weed that has leaves below the 

 surface, and also leaves on the surface. Those below 

 are narrow, and those above the surface are broad. 



6. This, too, may be one reason why leaves that are 

 much cut are generally near the ground where the 

 light maj' be shut off by other plants. Even in a 

 healthy plant, the lower leaves, when shaded by the 

 later leaves, tend to dwindle away. You know how 

 the lower leaves in a wheat plant get yellow and wither 

 even when the plant is growing strongly. This is 



