THE STEM 39 



rings. Examine a stem of several years' growth, and 

 count the annual rings.* (See fig. 19). 



8. The stem as a sap-channel. And now we have 

 to look at the second duty of the stem. How does 

 the stem serve as a sap-channel? And, first of all, 

 you must remember that there are two kinds of sap 

 to be carried — the sap from the roots, and the sap 

 from the leaves. 



9. Root-sap tubes. The raw sap from the roots 

 comes up through tubes in the new wood ; and so we 

 shall call the new wood the sap-wood, to distinguish 

 it from the hard old heart-wood. The root-sap runs 

 up the tubes in the sap-wood to be mixed with the 

 food gathered by the leaves from the air. Out of this 

 mixture is made the ripe sap, which carries to the 

 root the power to make new roots, to the wood the 

 power to make new wood, and to the buds the power 

 to make new shoots and leaves and flowers. And 

 where does this leaf-sap find channels ? 



10. Leaf-sap tubes. The tubes that carry down the 

 leaf-sap are placed in the inner bark. You see, then, 

 that the leaf-sap tubes are not so deep in the tree as 

 the root-sap tubes. But how, you ask, can the 

 leaf-sap get into the inner parts of the stem ? 



11. The silver-grain. Take the cut shoot shewing 

 two-year old wood. Use your lens, and you will see 

 rays running from the bark to the pith (fig. 21). These 

 rays are called by cabinet-makers silver-grain, and 

 they serve to carry the leaf-sap inwards from the inner 

 bark. You will notice that the rays pierce the bark. 

 They run right inwards to the pith, and are therefore 



* In one growing season there may be a ring for the spring growth, and 

 another ring for a second period of growth in late summer or in autumn. 

 Several rings produced in one season are easily seen in the beet. 



D 



