THE NUTRITIVE ORGANS OF PLANTS 47 



1. Which of the three regions (bark, wood, and pith) found in 



the young stem can you readily distinguish ? Which 

 of the three becomes very much thicker and harder as 

 the stem grows older ? Which is very small in quan- 

 tity when compared with the young stem ? 



2. The curved layers of wood in the cross section are known as 



annual rings, so called because usually only one ring is 

 formed each year by the cambium layer. How many 

 years of growth are shown in the piece of wood you 

 are studying ? 



3. The lines in the cross section extending like the spokes of a 



wheel are the pith rays or medullary rays. Describe 

 the appearance of these rays. The shining, lighter 

 colored surfaces (to which the beauty of "quartered 

 oak" furniture is due), that appear in the longitudinal 

 sections of oak wood, are the pith rays. Find pith 

 rays in the middle surfaces of some of the oak pieces 

 you are studying, and describe them. 



4. Make a Jarge diagram of the cross section of the piece of 



wood you are studying. Label bark, wood, annual 

 rings, medullary or pith rays. 



60. The structure of the corn stem. Laboratory Study 

 No. 32. (Optional.) 



Cut pieces about two inches in length from full-grown corn stalks, and 

 split each piece in halves. (If necessary these pieces may be preserved 

 from year to year in 4 per cent formalin or in 70 per cent alcohol.) 



Examine the cross and longitudinal sections of corn stem. Find 

 the rind (the outer layer), the woody bundles or fibers (thread-like 

 structures), and the pith (material between the bundles). 



1. Thrust your pencil point into the pith; is this material hard or 



soft? 



2. Pull out one of the woody fibers ; is it tough or tender ? 



3. Push your pencil point into the rind ; is it hard or soft ? 



4. Make a drawing (X 2) showing both cross and longitudinal 



surfaces. Label rind, woody bundles, pith. 



