10 



AGRICULTURE. 



The stalk is compact and strong, built for holding up a 

 heavy weight. When young the stalk and branches are green 

 in color; as they grow older the color becomes darker and 

 duller, and the soft, smooth skin changes to hard, rough bark. 

 The stalk and branches are much stiffer than the roots ; if they 

 were as pliable as the roots they would not be able to hold 

 themselves up in the form that we see. Most plants, however, 

 are pliable enough to yield to strong wind and thus avoid being 

 broken. The last thing to be noticed here in regard to them 

 is that what is called " the grain " goes along and not across 

 the branch and stalk. We can split a piece of wood along its 

 grain, but we have to saw or break it if we wish to divide it 

 across the grain. What would be the effect of a strong wind 

 upon plants, trees, forests, if the grain ran across instead of 

 along the stalks, limbs, trunks, and branches ? 



The most noticeable points in connection with leaves are 

 their shape, their number, and their color. The leaf is generally 

 flat and very thin. Its outline or form varies with different 

 kinds of plants. Contrast the thick, needle-shaped leaf of the 

 pine and the thin, long, pointed blade of grass with the leaves 

 of the oak, maple, basswood, and willow. 



Take a green maple leaf ; draw its outline ; trace the frame- 

 work upon which it is formed. Then glue or paste it between 



two sheets of paper or cloth 

 and dry carefully. Pull these 

 two sheets apart and thereby 

 split the leaf. We thus see 

 that the leaf is a thin web 

 stretched upon a framework of 

 fine branches, and we observe 

 that the branching of these 



Fig. 12. Section of a Leaf. A , row of cells ., r , , r ,,,- 



to.ming skin on upper side; B, row of ribs of the leaf vanes m differ- 



cells next to skin ; 1), next row of cells; , j / i c -u 



C, air spaces in leaf; E, inner portion of 6nt kinds Of leaves ; further, 



cells filled with sap; F, row of cells form- ., . .1 > .1 i_ r :, 



ing under skin or leaf showing mouths that though the leal IS 

 or openings (stomnta). 



