THE STEM 103 
e, Fig. 119; (2) the primary cortex, c; (3) a ring of fibro- 
vascular bundles, f; and (4) a central cylinder of paren- 
chyma, p. In some specimens there will be a fifth region, the 
pith, which will appear in 
the section as a white cir- 
cular spot in the center of 
the parenchyma. 
In specimens a little older 
than the one shown in Fig. 
119, a narrow circular line 
will be seen running through 
the ring of bundles nearly 
midway between their inner 
and outer extremities, con- 91%! _ Transverse, section of 
necting them into an un- vascular bundles not completely united 
broken diréle around the Go") ie mm ecdas tendies 
central cylinder. This is 2? central cylinder of parenchyma. 
the cambium layer, which supplies the vascular region with 
materials for new growth, and thus enables dicotyl stems to 
increase in diameter by the successive addition of fresh 
vascular rings from year to year. 
Examine in the same way a vertical section, and find the 
parts corresponding to those shown in Fig. 119. Make en- 
larged sketches of both sections, labeling the various parts 
observed. 
116. Minute structure of a dicotyl stem.— Place suc- 
cessively under a high power of the microscope thin trans- 
verse and longitudinal sections of the stem just examined, or 
such other specimen as the teacher may provide. Bring one 
of the fibrovascular bundles into the field, and try to make 
out the parts shown in Figs. 120 and 121. The corresponding 
parts in the two sections are indicated by the same letters. 
Notice the cortex, R, on the outside and the pith, M, on the 
inside ; between these, the cambium, C, the xylem, or woody 
tissue, included between the radiating lines X, and the newer 
tissues composing the phloém between the lines P. The 
