54 ELEMENTS OF BOTANY. 
Examine each thin section first with a power of about 25 diameters, 
then with a power of from 100 to 200 diameters. With the lower power, 
sketch a one-year-old section, labeling in your sketch : 
(a) The corky layer of the bark. 
(b) The green layer. 
(c) The masses of bast fibres. 
(d) The wood, with the medullary rays and vessels. 
(e) The pith. 
Fie. 41. — Cross-Section of a Three-year-old Linden Twig. (Much magnified.) 
P, epidermis and corky layer of the bark; Phl, bast ; C, cambium 
layer ; JR, annual rings of wood. 
After examining this section with the higher power and noting par- 
ticularly the appearance of the wood-cells, replace it by a section of stem 
at least four years old. 
Sketch this as seen with the low power, then substitute the higher 
power and study the inner bark, noting especially the masses of very 
thick-walled bast-cells. 
What are the principal differences between the structure of the apple 
twig, so far as you have examined it, and the structure of a linden twig, 
as shown in Fig. 41 ? 
