STRUCTURE OF THE STEM 



69 



■which constitutes the outer layers of the bark of cherry or birch 

 branches two or more years old. Sketch the roundish or oval 

 spongy lenticels on the outer surface of the bark. How far in do they 

 extend ? Examine (6) the green layer of bark as shown in twigs or 



di-' 



Pig. 41. One Bundle from the Preceding Figure, (x 100.) 



w, wood-cells; d, ducts. The other letters are as in Fig. 40. Many 

 sieve-ceUs occur in the region just outside of the camhium of 

 the bundle. 



branches of Forsythia, cherry, alder, box-elder, wahoo, or willow. 

 Examine (c) the white, iibrous inner layer, known as hard bast, of 

 the bark of elm, leatherwood, pawpaw, or basswood. 



86. Minute Structure of the Dicotyledonous Stem. — Study, first 

 with a low and then with a medium power of the compound micro- 

 scope, thin cross-sections of clematis-stem cut just before the end of 



