THE STEM. 21 



In many cases during the middle and latter part of the season, 

 the strands become numerous and join each other so as to 

 make a continuous ring or cylinder. This is 

 always true of shrubs and trees. 



5. The strands in stems of the Dicotyls con- 

 sist of wood and bast with a thin intervening 

 layer of delicate tissue, called cambium. The 

 woody portion of each strand is next to the 

 pith, and the bast portion is always toward 



the surface of the stem. Therefore when the strands become 

 numerous and large enough to join, their fusion will neces- 

 sarily result in the formation of a woody ring next to the 

 pith, a thin ring of cambium next to the wood, and a ring of 

 bast outside the cambium. The cambium layer will, each suc- 

 ceeding year, grow and produce an additional layer (or ring) 

 of wood — the annual rings thus revealing the age of the tree. 

 The bast is also constantly renewed by the cambium — the out- 

 ermost portion gradually dying, becoming furrowed, withering 

 away, or exfoliating as dead bark. 



Select some twigs and branches of any common tree, say the Linden, and 

 make thin transverse sections. Those from twigs of one year's growth will 

 have the pith in the centre, a ring of wood adjoining, then a, rijig of bast, 

 with the original epidermis and cortex exterior to the bast. The sections 

 from stems of two years' growth will show the pith and two distinguishable 

 though cohering rings of wood. Likewise the age of the others will be indi- 

 cated by the number of rings of wood-growth. Notice the narrow radiating 

 lines of tissue, some of them beginning at the pith. These are the Medul- 

 lary Bays. Use the pocket lens. Draw enlarged figures of the sections. 

 Make sections of twigs of various other species and compare the relative 

 size, shape and color of the pith, the distinctness of the annual rings and 

 the differences in the medullary rays. 



6. The Buds on twigs and branches are disposed regularly, 

 either at points opposite — rarely in a whorl of three or more 

 —or but one at a node (joint). They are at approximately 

 regular intervals and there is a terminal bud to each stem or 

 twig. Below each of the lateral buds will be seen a scar (leaf- 

 scar), indicating that each was developed just above (that is, 

 in the axil of) the leaf; the buds are therefore axillary and 



