72 APPLIED BIOLOGY 



hard cell-walls remain. Examine a stained section (permanent 

 preparation, or stained as suggested in 68. In some of the cells 

 darkly stained bodies (nuclei) may be seen. These also are com- 

 posed of living matter, and as far as is known every living plant cell 

 has a nucleus. 



Carefully compare the section as seen with the microscope and 

 Fig. 48. Locate the thin-walled sieve-tubes in the inner layer of the 

 rind, and the surrounding bast-fibers. These tubes and fibers make 

 the rind "stringy." The function of the sieve-tubes is to conduct 

 fluids down the stem ( 103). 



Note in the wood of the stem certain groups of large empty cells. 

 These are really groups or bundles of tubes (wood-tubes) and strong 

 fibers (wood fibers) extending up and down the stem. These are 

 the bundles of tubes and fibers which make the wood "stringy," 

 as already noted. 



The tubes and fibers of the rind are separated from those of the 

 wood by the cambium (Fig. 48). All the tubes and fibers taken 

 together constitute the fibro-vascular bundles, meaning bundles of 

 fibers and tubes. They will be studied more carefully in other kinds 

 of stems later. 



The work or function of the fibers of the wood-bundles may be 

 discovered by bending the stem to test its rigidity and by pulling to 

 test its strength. The function of the wood-tubes is shown by the 

 following experiment : 



(D or L) Cut off a young bean stem and stand it in a bottle with 

 red ink (eosin solution with water). After a half-hour, carefully 

 strip off the bark in various places in order to see the red color in the 

 woody part of the stem. Also cut across the stem in various places. 

 It is obvious that liquids go up the stem in the wood-tubes. 



The Bean Buds 



71. Position and Kinds of Buds. At various places on 

 a bean plant are buds, which will unfold later. Some of these 

 buds will form flowers, and hence are called flower-buds; 

 others will unfold as leaves and are therefore leaf-buds. At 

 the ends of the main stem and its branches are terminal buds 

 which, by growth, lengthen the stem and branches. If 

 the terminal bud of the main or a branch stem be destroyed, 

 lengthening of the stem will cease. For this reason gardeners 



