THE LEAVES 69 



have found that a round iron rod placed across a 

 stream will not bear the weight of a bridge so well as 

 a girder. By using this plan for umbrella-ribs, we 

 lessen the weight and increase the strength. You will 

 find a good example of the plan in the palm-tree leaf 

 which is one of the heaviest of leaves. How strongly 

 a leaf holds on to the stem you will find out if you try 

 to pull one off. 



3. The leaf-blade. A leaf that turns its face to 

 the sun to catch the light is generally flat and broad. 

 In a leaf-blade like this the upper side differs in look 

 from the underside. We have seen that the upper and 

 under sides have different kinds of work to do ; and 

 from our peep inside of a leaf perhaps you can guess 

 why the lower surface is of a lighter green than the 

 upper surface. 



4. A leaf, on the other hand, that holds itself erect 

 in the air is generally long and narrow, and has the 

 same look on both sides. Such a leaf looks alike on 

 both sides because both do the same kind of work. 

 Large, broad leaves would be out of place in a meadow 

 where a thousand plants are trying to get up into the 

 light ; and so we find that grasses have generally long, 

 narrow erect leaves. Notice, too, that some of these 

 small plants that are much crowded have leaves cut 

 into a fine network of leaflets. For shrubs and trees 

 that have to stand up in the wind, these deeply-cut 

 leaves would not be strong enough ; and so in high 

 shrubs and in trees we generally have leaves that are 

 not deeply cut.* The leaf, you see must have strength 



* This applies particularly to the soft-leaved deciduous plauts that cast 

 their leaves every year. Among the plants that hold their leaves through 

 the winter there are many exceptions, as the wattles. Evergreens have 

 tough leaves that can stand the wind. 



