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 (0) the green layer of bark as shown in twigs or 
Fic. 41. One Bundle from the Preceding Figure. (x 100.) 
w, wood-cells; d, ducts. The other letters are as in Fig. 40. Many 
sieve-cells occur in the region just outside of the cambium of 
the bundle. 
branches of Forsythia, cherry, alder, box-elder, wahoo, or willow. 
Examine (c) the white, fibrous 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 
