The Work of the Leaves 



colored pigments from the full glare of the sun. Some leaves have 

 wool or silk growing like the pile of velvet on their surfaces. These 

 hairs are protective also. They shrivel or blow away when the 

 leaf comes to its full development. Occasionally a species retains 

 the down on the lower surface of its leaves, or, oftener, merely in 

 the angles of its veins. 



The folding and plaiting of the leaves bring the ribs and veins 

 into prominence. The delicate green web sinks into folds between 

 and is therefore protected from the weather. Young leaves 

 hang limp, never presenting their perpendicular surfaces to 

 the sun. 



Another protection to the infant leaf is the pair of stipules 

 at its base. Such stipules enclose the leaves of tulip and magnolia 

 trees. The beech leaf has two long strap-like stipules. Linden 

 stipules are green and red — two concave, oblong leaves, like the 

 two valves of a pea pod. Elm stipules are conspicuous. The 

 black willow has large, leaf-like, heart-shaped stipules, green as 

 the leaf and saw-toothed. 



Most stipules shield the tender leaf during the hours of its 

 helplessness, and fall away as the leaf matures. Others persist, 

 as is often seen in the black willows. 



With this second vernal leaf fall (for stipules are leaves) the 

 leaves assume independence, and take up their serious work. 

 They are ready to make the living for the whole tree. Nothing 

 contributed by soil or atmosphere — no matter how rich it is — 

 can become available for the tree's use until the leaves receive 

 and prepare it. 



Every leaf that spreads its green blade to the sun is a labora- 

 tory, devoted to the manufacture of starch. It is, in fact, an 

 outward extension of the living cambium, thrust out beyond the 

 thick, hampering bark, and specialised to do its specific work 

 rapidly and effectively. 



The structure of the leaves must be studied with a microscope. 

 This laboratory has a delicate, transparent, enclosing wall, 

 with doors, called stomates, scattered over the lower surface. 

 The "leaf pulp" is inside, so is the framework of ribs and veins, 

 that not only supports the soft tissues but furnishes the vascular 

 system by which an incoming and outgoing current of sap is kept 

 in constant circulation. In the upper half of the leaf, facing the 

 sun, the pulp is in "palisade cells," regular, oblong, crowded 



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